How Many BTU Do I Need? (Air Conditioner Room Size Calculator)

There are several metrics you should consider before buying an air conditioner. You have different EER and SEER ratings, power, amperage, voltage, and so on.

The most important metric is the cooling capacity (measured in BTU/hr). It denotes the size of your air conditioner.

BTU meaning: British Thermal Unit or BTU/h is a unit that determines the cooling/heating power of an HVAC device (air conditioner, furnace, etc.).

What is BTU is an AC unit? Simply put, it’s the capacity or power of the AC.

The bigger the BTU, the more cooling effect an AC unit can provide.

Here is an example of how you can calculate how many BTUs you need to cool down a 500 sq. ft. area with 8 feet ceilings, average sun exposure, average climate, and not including kitchen (you can find this BTU calculator below and use it for your situation; with 4,000-24,000 BTU room size table):

example of size of air conditioner calculator in btu h


In short, you would need a 10,000 BTU air conditioner.

How many BTUs do you need to cool down certain square footage of space properly?

There are only 2 rules:

The BTU needed to cool down a room of known footage that can be calculated. According to The U.S. Department Of Energy recommendation for the size of room air conditioners:

“…an air conditioner generally needs 20 BTU for each square foot of living space.”

Based on room size, ceiling height, and other conditions, you can calculate how many BTU air conditioner you need:

Air Conditioner BTU Calculator

Calculated BTU:

0.00 BTU


As you can see, the sq ft to BTU converter neatly gives you an idea of what size of air conditioners you should be looking at in an ‘sq ft to BTU’ kind of way.

measuring rooms for air conditioner btu size
Roughly measure the places in which you want to enjoy the cool air thanks to your new AC unit.

If you want to properly cool down a 300 square foot area (or room), you need a 6,000 BTU air conditioner. Obviously, the problem arises when you have a tiny 12×12 room, for example. According to the US Department of Energy directive, an air conditioner’s most appropriate size would be 2,880 BTU unit. The best you can do here is to buy a small 5,000 BTU window or a small 8,000 BTU portable AC unit (more about the smallest AC units here).

The trendy portable air conditioners, for example, have a cooling capacity of 6,000 BTU to 14,000 BTU. According to Go Downsize, the average size of studio apartments in the US is about 500 sq ft. That means that for a small apartment, you don’t need expensive central air conditioning. You can install an average-sized 10,000 BTU portable air conditioner, which will save you tons of money.

Pro tip: Always buy a little bigger AC unit than this recommendation. Example: When you use the BTU calculator below and get, let’s say, 10,000 BTU for a 500 sq ft area, start looking for a 12,000 BTU air conditioner. Your electricity bill will be a little higher, but you won’t need to sweat if you bought an AC unit that’s too small.

To better illustrate what size of an air conditioner you need, let’s have a look at a BTU chart:

Air Conditioner BTU Chart; With 12,000 BTU (1 Ton) Room Size Example

Question: What is the 12,000 BTU air conditioner room size? 12,000 BTU is equal to 1 ton; we’re talking about 1 ton AC room size.

Answer: Using the EPA’s 20 BTU per sq ft rule of thumb, the room size of 12,000 BTU air conditioners is 600 sq ft. Equally, 1 ton AC room size is about 600 sq ft.

Here is a table with rough room size estimates for air conditioners with different cooling capacities to help you out:

Cooling Capacity (BTU):Room/Area Size:Examples:
4,000 BTU air conditioner room size:100-200 sq ft10x10 room, 12x12 room, 14x14 room
6,000 BTU air conditioner room size:200-300 sq ft16x16 room, tiny apartment
8,000 BTU air conditioner room size:300-400 sq ft18x18 room, 20x20 room
10,000 BTU air conditioner room size:400-500 sq ft22x22 room, small studio apartment
12,000 BTU air conditioner room size:500-600 sq ft24x24 room, average studio apartment
14,000 BTU air conditioner room size:600-700 sq ft2 rooms, small apartment
16,000 BTU air conditioner room size:700-800 sq ft2 rooms, average apartment
18,000 BTU air conditioner room size:800-900 sq ft3 rooms, above average apartment
20,000 BTU air conditioner room size:900-1,000 sq ft3 rooms, larger apartment
24,000 BTU air conditioner room size:1,000-1,200 sq ft4 rooms, large apartment

Again, when narrowing down your choice of an air conditioner, knowing how big an area you need to cool is your best friend. Based on that, you can calculate sq ft to BTU and immediately know what range of BTU values your perfect AC unit should be.

If, for example, you buy a 14,000 BTU portable air conditioner to cool down a 12×12 room, you will have a chill cold room and more than $100/year unnecessary cost on your electricity bill.

Perfect BTU Air Conditioner For Room Sizes

As recommended by The U.S. Department of Energy, the ballpark figure is 20 BTU per sq ft. That is a very good estimate already.

The simplest BTU calculation formula for an air conditioner looks like this:

BTU = Number of sq. ft. * 20

However, to get a perfectly-sized air conditioner with just right enough cooling power and no energy overspending, you should consider some additional factors. These are:

  1. Room height.
  2. Local climate.
  3. Sun exposure.
  4. The number and size of the windows.

The BTU calculator and chart work best for standard room height. Obviously, if you have a tall ceiling (older buildings have +10 ft ceilings), you have to add a bit of cooling power in BTU.

There is also a difference if you live in Texas or New York. The local climate in Texas is, on average, hotter, and therefore you should need an air conditioner with a few 1,000 BTU more.

The same goes for sun exposure. If the room or area you’re looking to cool down is generally facing the sun, you will need a bigger air conditioner.

Additionally, the walls do block the sun very effectively. Windows don’t. If you have big windows and many of them, the sun will heat your house more.

In summary, when do you need an air conditioner with higher BTU than standardly recommended:

  1. If you have high walls.
  2. If you live in a hot climate. Examples: California, Texas, Florida, New Mexico, and so on.
  3. If the particular room you want to cool down is facing the sun more often than not.
  4. If you have an above-average size and number of windows.

Example: If you have a 500 sq ft sun cabin near Texas with many glass windows, you should be looking at 10,000 BTU air conditioners (as recommended). It would be best if you were looking at 14,000 BTU portable air conditioners, for example.

What Does BTU Mean In Air Conditioners (Summary)

BTU in air conditioners is simple a metric of how much cooling effect that particular AC unit can produce.

We want an air conditioner that has just the right amount of cooling effect. That’s why by knowing the square footage of the area we want to cool down, we can calculate how many BTUs should our air conditioner have.

The equation for ‘sq ft to BTU‘ is quite simple – multiply the sq ft with 20. That means that a 500 sq ft room needs a 10,000 BTU air conditioner. Of course, do make sure to buy an AC unit that is a bit stronger if you have high ceilings, live in a hot climate, and have an above-average sun in those rooms.

For smaller spaces (example: camping air conditioners for tents), you can use portable battery-powered AC units.

You should use the BTU calculator when choosing different types of air conditioners, including:

Note: Evaporative coolers and mini personal air coolers do not produce a cooling effect that can be expressed in BTU. They use water evaporation instead of the refrigerant-based system to provide a cooling effect.

We hope this helps. If you have any questions about your particular room or area you’re buying an air conditioner for (and don’t know how many BTU ones you should take), you can ask in the comments, and we’ll try to give you an answer as soon as possible.

152 thoughts on “How Many BTU Do I Need? (Air Conditioner Room Size Calculator)”

  1. I have a 15 ft by 15th room with a 9ft ceiling. This room has a door way that goes into another 12 by 13 room.the door way is average size. What btu would you recommend.thank you for your time.

    • Hello David, 15×15 and 12×13 rooms have a combined area of 381 sq ft. Given the additional doorway and above-average ceiling height, you’re looking at a 9,000 BTU unit. 10,000 BTU with an above-average airflow (above 250 CFM) would be a safe bet. Hope this helps.

      • Hello. I need help finding the correct portable a/c. First off, do we pay attention to the first or second rating on a portable a/c unit labeled 10,000 btu(6,600doe btu). My apartment living room is 187 square feet, has 3 small windows, 8 ft tall ceilings and three doors leading to restroom, bedroom and kitchen. Only two people reside here. The room is south and East facing. And I live in Los Angeles,CA. Your guidance would greatly be appreciated.

        • Hello Arturo, 10,000 BTU might just cut it. According to the EPA’s conservative rule of thumb – 20 BTU per sq ft – you would require even less than 10,000 BTU. However, given that you’re based in southern California, with a south and east-facing apartment, 12,000 BTU or even 14,000 BTU portable AC might be necessary to adequately reduce the temperature at low-to-medium humidity levels. You can check out some portable air conditioners with high energy efficiency here.

  2. I am researching the most efficient portable room air conditioner for a 2nd floor, sunny bedroom. The 13’2” by 14’5” bedroom room has cathedral ceilings, a SW facing window that measures 48” by 56” and one occupant. Due to HOA restrictions and a sliding glass window, I plan to get a portable air conditioner. I’ve read about dual hose conditioners and not sure if that’s the best way to go. I’m not sure how to calculate the necessary BTU’s needed. Can you help with any thoughts on this? Thank you, Sue Harig

    • Hello Sue, the 13’2” by 14’5” room has about 190 sq ft. Let’s assume that the cathedral ceiling has a height of 13 ft. Such a bedroom has the same volume as a 310 sq ft room with an 8 ft ceiling height. That would, roughly speaking, require a 6.200 BTU portable AC unit. With that big sliding glass window and a lot of sun, the safe estimate for the most optimum AC unit would be 7.000-8.000 BTU.

      The dual hose portable air conditioners have two key advantages: superb energy-efficiency and they don’t lower the pressure inside the room while running. However, they tend to be bigger – 14.000 BTU or so. If you can find a 8.000 BTU dual-hose one, that would be a very optimum choice. Hope this helps.

  3. Hi David , I have a 25×17’ room with 8’ ceilings in all
    Adjacent hallway with 30 “ doorway hallway is 9×5
    Then doorway into lr and dr 30×21
    There is a wall between lr and dr with a 6 ‘ doorway
    How many btu would I need

    • Hello Peggy, for a 25×17 room (425 sq ft), you would need a 8.500 BTU portable AC. If you add 9×5 hallway (45 sq ft) and LR + DR 30×21 (630 sq ft), the total calculated area is 1.100 sq ft. Roughly speaking, you would need 22.000 BTU cooling power. Portable AC units will hardly handle it, window units or mini split units could do that job well.

  4. Thank you for the useful advice. My small apartment has openings in the wall for AC in the living room and the bedroom, thus I am debating whether to get one 14,000 BTU AC or two smaller ones. Any advice on the subject is appreciated.

    • Hello there, if you need 14,000 BTU AC, one window unit or one mini-split unit would be the best choice. AC units above 15,000 BTU usually need an electric upgrade; which you won’t need here. On the other hand, you can invest in two portable AC units, each of 7,000-8,000 BTU, but those can take some space and need to be vented out of the window. The most elegant solution would be a 14,000 BTU mini-split unit.

    • I have an area that is 850 sq feet and another room that is 300 sq ft. I want to purchase a unit for each area. How many BTUs do I need for each area and how big a condenser will I need to accommodate both with a multi unit condenser?

      • Hello Ruth, for 850 sq ft you would need a 17,000 BTU device and 6,000 BTU device for the 300 sq ft room. The best option would be to use a 2 zone mini split AC unit (1 outdoor unit with 2 indoor units, one in each room). 2 zones should have a capacity of 17,000 BTU and 6,000 BTU respectively. Such a combination, quite frankly, is hard to find; the most common 2 zone unit is 12,000-12,000 BTU.

  5. Hi there. Question… I’m living in a one bedroom apt in NYC. The AC unit will be for our living room. The living room itself is about 20’7″ x 12.1″. However, it has large windows and on the other side of the living room, there is a kitchen (that doesn’t have any AC). Your advice would be much appreciated!

    • Hello Grace, for the (roughly speaking) 350 sq ft living room you would need a 7,000-8,000 BTU AC unit. However, the kitchen is additional space and for kitchen you usually have to add 4,000 BTU. All in all, 12,000-14,000 BTU would make sense in this situation. You can opt for portable or window AC unit; mini-split unit would be a bit too much.

    • Hello Jackie, 16 x 14 room is 224 sq ft. If we assume a 9 ft high ceiling, average climate and average sun exposure, you’re looking at 5,000-6,000 BTU units. For this size, a smaller portable air conditioner would be most appropriate. You can find some of the best portable AC units here.

  6. I have a 16×16 bedroom on the second floor with 8′ ceilings. My current wall unit is 15 years old and has ALWAYS made the room feel damp. I was told the unit is too big for our size room. I went to local store to size one more appropriately and was told the Frigidaire FFRE153ZA1 15,000 BTU’s is the right one. Of everything I read online, it seems to me that this is too big? Am I correct? What size wall unit would best suit my needs and what Frigidaire wall mounted model am I looking for?

    • Hello Michael, 16×16 bedroom has a total area of 256 sq ft. That means a 5,000-6,000 BTU would be enough. You are right; the 15,000 BTU unit is definitely an overkill for a single room. Conservative choice would be the old Frigidaire FFRA051WAE 5,000 BTU. However, given that you have problems with high humidity, a stronger Frigidaire FFRE0833U1 8,000 BTU makes sense (it comes with 1.7 pints per hour dehumidification; it can draw more than 40 pints of water per day). Hope this helps.

      • I have a 26 by 30 room 10 ft walls plus 3 ft to ceiling sun hits direct it’s 780sqft how many btus is recommended going to install two ceiling fans thanks

        • Hello Carlos, with 10 ft ceiling the two fans is a good idea. The room has quite a volume; you would need about 25,000 BTU devices. 2 12,000 units might do the trick as well.

          • So I can just put a 30000 btu minisplit would that work is a 36000 btu unit too much thank you

          • Hello Carlos, the 30,000 BTU mini-split will do the job very well. It’s always better to have a little bit bigger capacity than a little bit too weak a unit. 36,000 BTU would be an overkill.

  7. I live in New York. My small apartment is 600 square feet but is broken up into 2 bedrooms, 1 living room, 1 kitchen, 1 hallway, bathroom. I have lots off walls and ceiling is just under 9 feet high. I want to buy a mini split ac system. Would an 18000 BTU unit split into 9000/9000 work? 1 in the front bedroom, 1 in the back bedroom…and leave doors open during the day?

    • Hello Andrew, several rooms, hallways, and kitchen do add to the overall BTU cooling power. You’re right; you would need at least 15,000 BTU device – a 18,000 BTU would be perfect. Two-zone 9000/9000 mini split would be the perfect solution here. You do have to have the door open in order to ensure smooth air circulation. It seems that you already have exactly the right idea what to do.

  8. Live in Central California Modesto it gets super hot in the Summer I’m in a 23 by 25 master using a 5,000 btu. I’m thinking of getting an 8,000 btu the 5,000 btu just isn’t cutting it. I have three windows one being a huge 12 by 6 and it’s located to the west the whole window gets very hot midday. Should I get the 8,000 btu?

    • Hello Edward, you’re correct, the 5,000 BTU unit is not enough. 23×25 master bedroom is 575 sq ft. Given that you’re in sunny California with 3 windows, even the 8,000 BTU might not be enough. For your situation, a 12,000 BTU or even 14,000 BTU would be recommended.

  9. I have an enclosed patio room, it is 20 by 15′ with large windows on three sides. What size portable uni
    t do I need?

    • Hello Harold, for a 300 sq ft patio you would need 6,000 – 8,000 BTU unit. Portable air conditioner would probably be the most convenient.

  10. Good Morning. I have a office room size of 22ft x 30 ft with ceiling height of 9 ft. No direct sunlight but evening sun rays through two glass window. How much BTU do I need to cool the room? Is there any standard that the temperature of the room should within a particular time and what other specifications do I need for a AC while buying like CMH, Cooling Capacity.

    • Hello Sivaram, a 660 sq ft room with low sun exposure would need, roughly speaking, 14,000 BTU AC unit. The only standard for BTU size is the EPA recommendation of about 20 BTU for every 1 sq ft of a room; other factors may apply as well. In your situation, a 14,000-15,000 BTU should do the job well.

    • Hello Kerwyn, we have to do a bit of sq m to sq ft conversion here. 100 m2 living room is equal to 1076 sq ft. With +4,000 BTU for the kitchen, you’re looking at 28,000 BTU device. 30,000 BTU to be safe.

    • Hello James, the usually 15,000+ BTU mini split units need run on 220V. If you’re looking at a 12,000 BTU 220V model, there is a chance the same mini split is available with 115V and double the amperage. The key here might be the heater. If it’s a 18,000 BTU heater, for example, the whole unit will usually need 220V.

  11. I have a Sunroom that’s 17 Ft. by 17 Ft. with a ceiling height 8 1/2 Ft.
    3 of walls are all glass top to bottom. ( room built 1963 ) It also has a very heavy Sun exposure. Located above this added on room is an open attic… can you help

    • Hello Hugh, that’s one hell of a room. Standard 300 sq ft room, for example, would need at least 6.000 BTU device. With the added 1/2 ft of the ceiling and the 3 windows, you should probably check out 10,000 BTU units.

  12. Hi,
    I’m looking to use a portable air conditioner in my garage. Its 683 sq ft with an 11 ft ceiling. I live in central North Carolina. Direct sunlight on insulated garage doors during the afternoon. Garage walls are foam insulated. Four windows, three of which get direct sunlight. Windows are doubled pane. Cement floor. According to your BTU calculator I would need 18,837.5 BTUs. Not sure if they make that size AC in a portable? So, would two 10,000 BTUs work or 14,000 BTUs work just as well?

    • Hello Daryl, the biggest residential portable AC units have a maximum cooling capacity of 15,000 BTU. It’s an electrical thing; if you want 15,000 BTU+, you would need 220V instead of 115V, or alternatively, you would have to double the Amps, which is not ideal. In your situation, you would probably need two units, yes. 2 x 10,000 BTU would make sense. Maybe a combination of 14,000 BTU and 8,000 BTU would be smarter; you only run 14,000 BTU most of the time but during a really sunny day, you also turn on the 8,000 BTU unit.

  13. Hi, I’d like to change window AC unit to a new one. The old one I’m using is 5,200 BTU and it’s not cold enough for summer and now it fails to work properly. My room size (long shape / Studio with kitchen) is 32×11 ft. ( 350 sq.ft.) with 8 ft ceiling, highly sun exposure side of the building (3 windows size: 3×5.2 ft ). I have 2 choices of AC 8,000 BTU or 13,000 BTU. ( someone has extra AC and offer 1 from these 2 to me).

    Which ones should I use? Consider from my information.

    I’ve checked online, it recommended 8,000 btu but with my room size & conditions(very sunny), some website said I should consider to add more BTU than a regular BTU calculation. I’m aware if I use 13,000 BTU, It probably cold more than enough but I concern about electricity bill.

    Normally, I use 20″ portable fan to help the air circulation for AC as well.

    Thankyou so much.

    • Hello Pond, your dilemma is understandable. An average 350 sq ft room would need a 7,000 BTU unit. However, the 3 big windows can really increase the size of the air conditioner you need.

      Of the two choices, 8,000 BTU would be the optimum one. It’s a big increase from 5,200 BTU and it will probably be much more cost-effective than 13,000 BTU device. The rule of thumb is to buy an AC unit that’s a bit bigger than what you actually calculate; in your case, that would be something like a 10,000 BTU device. However, if the choice falls between 8,000 BTU and 13,000 BTU, an optimistic view is that 8,000 BTU should do the job well without increasing the electricity bill significantly.

      • Thankyou very much for your suggestions and ideas. The 8000 BTU will be my final choice.

        I am also thinking to add window films like reflective one to help cut down the sunlight and the heat.

        Thankyou so much again!

  14. Hi
    I am living in the Caribbean, my entire house is 30 * 20 ft, one bed room is 11 * 9 ft floor to ceiling throughout the building is 9 ft. The house is elevated and has wooden floors now can you advise say if i should buy the 4000 BTU for my room or splurge and buy the 12,000/14,000 BTU for the entire house?


  15. I have a lanai 200 square feet with aluminum enclosure and acrylic windows. What size portable AC would work? In the summer here central Florida the room fells like an oven!

  16. Hi, I’m looking to replace a window air conditioner for a 240 sq ft living room with 8 ft ceiling and average sun in Connecticut. The room has a 48 in open doorway to a 90 sq foyer (directly opposite the window with the AC unit) and a 30 open doorway to a 200 sq ft dining room (to the side). The current 8,000 BTU unit does not cool the living room sufficiently. Could I go with a 10,000 or 12,000 BTU unit? Or do I need to get another unit for the dining room (which I’d prefer not to do, as I’m mainly looking to cool the living room)? Thanks for the advice!

    • Hello David, in most cases 8,000 BTU should be more than enough for a 240 sq ft room. However, in your situation with a big window area, the 8,000 BTU unit might struggle to achieve the required temperature. It’s better to be safe than sorry; given the high overall window area, the 12,000 BTU device would be a safer choice.

  17. It is so kind of you to field these questions.

    Here are the specs of my apartment:
    Ceilings: 8.5′
    Central hall area: 8′ x 5′
    Rooms off each side of the hallway:
    Living room: 13′ x 15′ (very warm—southern exposure, over the building boiler room)
    Kitchen: 9′ x 13′ (northern exposure, but warm because of the gas stove)
    Bedroom: 12′ x 12′ (northern exposure)
    Bathroom: 8′ x 8′ (northern exposure, I don’t bother to cool it)

    Up to now I’ve had window units in both the living room and the bedroom. A friend is suggesting that it’s possible to cool this kind of layout with only one window unit (which room?) & good fans strategically placed. I have my doubts. What do you think?

    Thank you!

    P.S. I live in southwestern Connecticut. Humidity is high and in recent summers the temperatures are sweltering for 6-8 weeks.

    • Hello Meg, the total area to cool down is 560 sq ft. According to the EPA, you would have to multiply that number with 20 to correctly size your air conditioner unit. Of course, other factors such as sun exposure and your location can significantly increase the size of the AC unit that would be most appropriate.

      Your friend is right. A 15,000 BTU or 18,000 BTU device could theoretically cool down the entire apartment. The fans are also useful in order to distribute the cooled air throughout the apartment. What size are the 2 window units that are currently installed?

      • Hello again,

        The living room unit is 6,500 BTU and the bedroom unit is 6,000 BTU. I use them only for those rooms. The BTUs are more than adequate for the spaces, but the units are too old to work properly and need to be replaced.

        The configuration problem I anticipate with using a single unit for the whole apartment is that the air flow from bedroom to living room involves passing through a narrow doorway and make a dog-leg turn. I look on fans as efficiency boosters, not as mandatory links in the cooling chain, if you see what I mean. Nor do I want to end up blasting the AC in one room but still getting an inferior result in the other.

        Cooling the living room and the kitchen as one consolidated space is a much easier proposition. Until this summer, I haven’t minded having a hot kitchen. But with the need to work from home now, it would be a huge benefit to have another fully habitable room.

        I’m investigating the Midea U Inverter window units because the position of the compressor should make for quieter functioning. They get excellent reviews, and the sturdiness of the mounting looks like it might save wear and tear on the units, given that I must install and uninstall them every year. Amazon has them in 8,000/10,000/12,000 BTU models.

        Here’s what I’m thinking now. Get two air conditioners. A less powerful one just for the bedroom, a more powerful one to handle the two hottest rooms (living room and kitchen) together.

        I need to keep an eye on the finances, but this is an infrastructure upgrade. 🙂 I’d like to get it right the first time and not have to think about the AC for another ten years!

        Thanks again for helping me to think this through!

        • Thank you for the insight; I’m sure it will be most helpful for everybody who is experiencing similar problems. In short, the logic you’re using is very sound, you know exactly what you’re talking about. Have a cool summer!

  18. Considering this is for a normal housing with wood structure. You should add a concrete duplex/apt for wall units and how much BTU is needed.
    I live in a concrete duplex my bedroom has a wall unit that is small and doesn’t cool at all. bedroom gets full sun all day, and at night the bedroom feels like a stone oven, there is no reprieve.
    The wall ac just died since it is 13 years old and landlord isn’t going to replace it, so, it is up to me, but all i see are window ac units and 5,000btu is too big for the wall opening.

  19. Hi,

    First of all, thank you so much for this website, it has so much useful information and I’m sure everyone who comes across it appreciates it very much.

    Here’s my question; I see that adding a kitchen to the analysis greatly increases the BTUs. For example, when I put in the specs for my apartment, 32 ft by 15 ft, 8 ft ceiling and heavily shaded, the BTUs come out to a little over 10,000. However when I checked off kitchen, it jumps up to over 14,000. Is that extra 4000 BTUs necessary whether or not the kitchen is actually being used? I am no cook and, except for using my microwave and toaster every everyday, I hardly ever use my kitchen except to go to the refrigerator to get something to drink or find something to heat up in the microwave. Is there something about the mechanics of the kitchen that will automatically necessitate an increase of 4000 BTUs or is there an assumption that the kitchen is actively being used, i.e. the oven is being used everyday.etc.

    Again, thank you for maintaining this website.


    • Hello Scott, thank you for your kind comment. The question is very on point; a rule of thumb is to add 4,000 BTU for the kitchen because people who have kitchen usually use it (kitchen appliances, oven, stove, even fridge all create surplus energy). There is nothing in the nature of the kitchen itself that would call for a more powerful air conditioner. If you don’t use your kitchen, you can forget about that 4,000 BTU. The BTU calculator is made with presumption that +90% of people use the kitchen regularly; hence the increased air conditioning demand.

  20. Hello,

    I am looking into installing a mini split but don’t know how big to get it. My kitchen is open to the living room with an attached hallway. I have a total of 5 windows. Kitchen is 17.5 X 8 living room is 16.5 X 12.5 and hallway is 17.5 X 3. All open and connected to each other. Please can someone help.

    • Hello Miguel, the square footage of the kitchen, living room, and hallway combined is about 400 sq ft. The minimum size of the mini split unit for 400 sq ft would be 8,000 BTU. However, for kitchen most HVAC experts add 4,000 BTU because of all the cooking, baking going on. Another thing you need to take into account is the length of the hallway; it’s 17.5 ft long. You might want to get an additional fan in order to create indoor airflow that will distribute the cool air evenly, even as far as the end of the hallway. All in all, 12,000 BTU mini split air conditioner would make a whole lot of sense in your situation.

  21. Hi, i have a tiny shed of 12′ x 32′ 8′ ft in height. But there is a wall in between, one room is 12′ x 18′. The other is 12′ x 14′,what would you recommend for less energy used. Any help will do thanks Manny

    • Hello Manuel, you would need an 8,000 BTU air conditioner. If there is a hole in that wall, the air-conditioned air will reach both rooms. If the wall doesn’t have a hole, you should opt for the smallest portable AC units. You can easily put it in the 1st room and then in the 2nd room. The smallest capacity for a portable AC unit is 8,000 BTU, you can check other small air conditioner choices here.
      For minimum electricity expenditure, look for AC units with a high EER rating (above 10). Hope this helps.

  22. I’m trying to figure out the BTU size for a mini-split I want to put in an addition to augment the central air. The room is 12 x 19.5 with an open ceiling 12′ high at the peak and 7.5′ high on the east & west sides. It attaches to the rest of the rancher thru a 6′ x 6.5′ opening where a patio sliding door used to be. That door is now on the west wall of the addition, The south wall has two 5′ tall x 4′ wide casement windows on either side of one centered 5 x 6 bay window. Then there is a 5 x 5 casement on the east wall.

    • Hello Bob, the space-wise structure you have there is quite complex. You should probably talk with an HVAC installation expert who can also recommend the best mini split to use, in addition to AC capacity (BTU). We have 1000s of experienced HVAC expert across the US, you can use this link to get an HVAC expert in your area to help you out. They’ll certainly know how to calculate that ceiling slope.

  23. Hello, I am trying to get an AC unit for my fifth-wheeler. It’s 32×9 in average (somewhere in between 280-340 sqft). The ceiling has a height of 8 ft. Do you think a 15,000 BTU unit would be an overkill? Also, I am considering that since it is pretty long (32 ft) 15,000 BTU could do a great job. Thank you

    • Hello Julio, for 280-340 sq ft, 15,000 BTU would be an overkill. You’re correct to be concerned about the 32 ft length; you want to have a conditioned air throughout the fifth-wheeler. The best solution here would be a 10,000 BTU unit with a strong airflow. Strong airflow – something above 300 CFM – is better for long spaces because it can push the air along the space much better.

  24. interesting problem with the Midea U-shaped inverter unit. As great as it is, unfortunately, it cannot be left in the window during cold winter. Midea owners manual (and Midea comments on Amazon) recommends that the unit be taken out and stored for winter. I confirmed this with Midea directly, and they said the “sensor” could be damaged by extreme cold, so its not even a case of shortened life expectancy. I suggested that most people in cold climates never remove their window units, especially heavy 10k BTU models. This is especially true for apartment dwellers, who also have no place to store big AC units. I fear that Midea will get lots of warranty calls next summer when these units fail. They will also lose lots of sales when people in cold climates realize they can’t leave them in window all year. Hopefully they can fix this.

    • Hello Jeffrey, thank you for the insight. Normally, it’s recommended to remove any window AC unit during the winter. There are two reasons for this; window AC units don’t isolate from the winter weather as well as windows and most homeowners like the improved aesthetics when they tuck the unit away for the winter (not the most appealing device to have on a windowsill). Furthermore, this will also increase the unit’s lifespan. So, all in all, it makes a lot of sense to pack any window AC unit away for the winter; it’s not actually a problem, it’s a well-thought-out recommendation.

  25. Hello.
    I just bought a little single wide in Texas. 2- 130ft sq bedrooms 1- 48sq ft bathroom, living room and kitchen 338 sq ft and ceiling is 7 ft. I am thinking of buying a mini split. Is it possible to just use one console to heat/cool the whole place? If yes, how many btu’s do you reccomend?

    Thank you:)

    • Hello Jessica, you’re looking to heat/cool about 700 sq ft, divided among 4-5 rooms, including a kitchen. You would need about 20,000 BTU device, or even a bit more. You’re correct; a mini-split heat pump is a perfect choice for your situation (just with 1 console). You can check out a number of the best 24,000 BTU mini-split heat pumps here, and read about how energy efficiency specs (SEER, HSPF) affect the electricity costs in the long-term.

  26. Hello! I just want to start out by saying this is an awesome website and super helpful.
    I have a 1050 sq.ft garage with 9 ft ceilings and no divided spaces. I plan on installing a 2.5 ton system, with 2 total head units, one on either side of the room to evenly circulate airflow through the large space. It is insulated very well with decent heat load as I live in California. I am just wondering if this should be sufficient for the space I’m trying to cool.

    • Hello James, thank you for the compliments. You have the right idea about the placements of the 2 head units; a 2.5-ton system will be enough for properly cooling your garage.

    • Hello Tommy, if we apply the EPA recommendations for 8 ft ceiling we get 640 sq ft * 20 = 12,800 BTU. Now, 18,000 BTU would definitely do the job but it might be an overkill. According to the calculation, the 12,000 BTU is nearly enough. Basements tend to be colder because they have less sun exposure and are located near the ground. 12,000 BTU might just cut it, especially if you have a 7 ft ceiling.

  27. I’m confused. I was informed my 10,000 BTU portable AC unit was not cooling my apartment’s front room, kitchen, hallway, total 380 square feet, because a 8,000 BTUs unit would be better. I have 3 large, sun drenched windows in the front room. The ceilings are 8 feet.

    • Hello Missy, 8,000 BTU is the optimum capacity. The 10,000 BTU would be overkill; it would cool the space better due to 2,000 BTU more cooling power but the electricity bill and the initial portable AC cost would be higher.

  28. Hello, my ac person recommends i put in a 12000 ac/heat system fujitsu, in apartment that has the following, living room = 225 sq/ft, master = 210 sq/ft, bedroom2 = 201 sq/ft, bedroom3 = 126 sq/ft, kitchen = 198 sq/ft entrance(common area between all rooms) = 97 sq/ft, all rooms have doors, for total of 1057 sq/ft TOTAL, 8ft ceiling height and he says that will be enough because not open concept, my question is, will the whole apartment feel cold, or some rooms maybe be hotter if I get it, will it be rushing or is 15 or 18 btu system overkill and cost wise will it be much more expensive to purchase and run day in and out, thank you for your time and help

    • Hello Walter, the basic EPA recommendation is that you would need 20 BTU for every sq ft. 1057 sq ft would, using this recommendation, need 21,140 BTU unit. The 12,000 will cool down a few rooms (living room + master + bedroom 2, for example) but not the whole apartment. You have to close the door somewhere in order to create a 500-600 sq ft isolated area.

  29. I am building a small L shaped home. One part is 48×20 that has the living room & a small office area, 3 bedrooms, 2 bathrooms. The other part is 20×16 open kitchen/dining area. How climate is mostly in the 80s year round and very humid (Hawaii problems?) What air cooling system would you recommend. I’m also on a tight budget. Thank you for your help

    • Hello Charlie, you would need about 30,000 BTU, maybe a bit more (Hawaii problems :)). Because you have the L shaped home with a number of rooms, you’ll need a number of units. The best option are the 3-zone mini-split units; you get 1 outside unit and 3 indoor air handlers you distribute evenly around the house.

      If you check those 3-zone mini-splits, you will see that the best one – with 36,000 BTU – is Senville SENA-36HF/T. That’s the most budget option you can get; it also has high energy-efficiency which means low running costs. Hope this helps.

  30. I’m looking at installing split system. My house is 4 bedrooms plus lounge/ dining and family/kitchen just wondering how many systems and what size( was advised by store that I would need 1 for each bedroom and possibly 2 others) Expensive!! But not sure if this will be correct??

    • Hello Tracy, for a big house with big rooms (bedroom, 2 other rooms), you can buy a multi-zone mini-split system. They can be quite expensive; a 3-zone mini-split with 3 x 9,000 BTU can quickly cost as much as $5,000. You can check the LM’s article about the best 3-zone mini-splits here to check for the most optimum units.

  31. My girls just moved into a small 2 bedroom house without ac. We need to decide on portable ac or a window unit.

    the living room and kitchen are next to each other and the 2 bedrooms are down a average size hallway.

    Living room is 17×12, kitchen is 10×15 and bedrooms are 10 x 13 and 11X15

    if the ac unit is placed in a window that faces the hallway and in between kitchen and living room, will the air conditioner cool the hall and the bedrooms too? luckily my girls unit, utilities are included.

    Also I love your calculator. In most literature I see it measured by square footage per room and that it wont cool anymore than that and it wont cool correctly if unit is too big for that room. this confuses me.

    I just need to know what size to get and where it is best to place it…

    • Hello Joy, thank you for your kind words. Between portable and window AC, it’s always best to buy a portable unit because you can move it around and find that perfect spot (on the hallway, for example). A window unit is always in 1 room and can’t be moved – if you put it in the living room, will the bedrooms be covered as well? These are the kind of issues you get with window ACs.

      The total square footage is about 650 sq ft. Normally, you would need a 13,000 BTU unit for that. If you account for hallways, a 15,000 BTU portable AC unit placed on the hallway between the rooms might be the most optimum option. For 18,000 BTU+ unit, you’ll need 240V voltage, keep that in mind if you decide on a bigger unit. You can check some of the best portable ACs with a high-efficiency rate here.

  32. If I’m living in Florida and have 14,000 btu ac how cold will that keep the room if its 90 degrees and the room is 12×10 and there 9 feet high ceilings

    • Hello Karl, sufficiently cool even in Florida’s heatwave. That’s a very small room and quite a normal-sized air conditioner. You can set the temperature as cold as you wish; the 14,000 BTU AC will handle it.

  33. Hello…I live in Mesa, Az and want to install a Mitsubishi mini-split for my garage.
    I want to be able to cool the garage down to 80 to 85 degrees from 100 to 110 degrees outside temp. 3 car garage, 9 foot ceilings, 660 square feet with one window…walls, ceilings and garage doors insulated…. is 18,000 BTUs enough?

    • Hello Marc, the conservative estimation by EPA is ’20 BTU per sq ft’; that’s for living areas, 8-foot ceiling, standard insulation, and so on. Even in those conditions, the safer way is 25 BTU per sq ft. For a 9 foot garage, 30 BTU per sq ft might be more appropriate. 660 sq ft * 30 BTU per sq ft = 19,800 BTU. With 1 window, good insulation, 18,000 BTU might just be enough, yes. You can check some of the air conditioners appropriate for the garage here, maybe it could help a bit.

  34. This subject can be much more complicated….
    My room is 16.5’x 9.6 with ceiling sloped from 7’ to 8’ . So let’s say 7.5’
    It has 3 windows that are roughly
    The roof is a very slight slope-almost a lean-too. So not much for attic space.
    It is a audio room / bedroom.
    So I have the heat load of the equipment to also consider.
    It is on the west side of house as well.
    I am also in central Texas!
    I have a 10,000btu window unit in there now that is just enough, but way too noisy. I have window coverings that are insulated.
    What do you recommend for a mini-split for 120v with no heat and is whisper quiet?
    Thank you
    It only

  35. Hey. I have 1000 sq foot house. Currently a small unit in living Room . on other side of the house with the bedrooms were unbearably hot and humid this past summer. Is it best to replace the one unit with 20000 btu’s or two smaller units since cooling multiple rooms?

    • Hello Selena, 20,000 BTU unit has the right size, and will deal both with hot and humid indoor air. However, 15,000+ BTU units require 220V voltage. If you will have to upgrade your electrical grid just for that, it might make more sense to buy an additional 12,000 BTU or 15,000 BTU unit. Together, they will also create a more homogenous cooling (without hot spots); this might be a problem with 1 20,000 BTU unit if it has a low airflow (measuring in CFM).

  36. Your site has given me a lot of ideas… but not fully addressing my specific need. I live in Southwest Florida and have a 12 x16 lanai with 8-1/2 foot ceilings that receives the sun most of the day. There are shaded non-glass windows (tax reasons) on two of the four walls. In order to maintain a reasonable comfort level, what size thru-the-wall A/C unit would you suggest? Thanks

    • Hello Ray, 12*16 is 192 sq ft; with a bit over 8 ft ceilings. In a normal situation, a 6,000 BTU would suffice. Add Florida, sun exposure, big non-glass windows to the equation and you’re looking at 10,000 BTU unit (just to be safe). You can check out the LG unit in our list of the best thru-the-wall AC unit.

  37. Hello, I’m looking for a solution for our new house with casement windows.  Ultimately, I know a mini-split system will be best, but it’s out of our budget right now.  So, we’re looking at getting several portable units with plexiglass window covers (with cutouts for the exhaust).  The master bedroom is on the 2nd floor, 425 sf, including the bathroom.  Mostly 8′ ceilings with one peaked area up to 12′.  I’m assuming a 12,000 or 13,000 BTU unit.  Another bedroom is 160 sf, so I’m assuming an 8,000 BTU unit.  We probably won’t run this one unless we have guests.  Now here’s the fun part- an open concept area with the living room, dining room, kitchen, plus the hall, laundry room, a half bath, and a full bath.  That area is about 900 or 1000 sf, with many windows and a cathedral ceiling in the living room up to 25 feet or more.  I’m thinking 3 units- one in the living room, one in the laundry room doorway in the hall (aimed at the kitchen), and one on the upstairs landing above the living room.  But I don’t know what size I’ll need for those 3 units.  Any advice?  Anything we need to be aware of for electrical systems?  Or single vs dual hose units?  We’re in the northeast US.  Thanks for your help!

    • Hello M, nice plan. Your calculations for the master bedroom with bathroom and another bedroom sound about right. The cathedral ceiling open concept area is fun indeed. 🙂 Calculating the full volume of that area is a bit complex. Let’s simplify it a bit; a 1,000 sq ft area with 16 ft average ceiling height. For that you would need somewhere between 40,000 and 50,000 BTU; depending on insulation, sun exposure, and so on.

      Portable units running of 110/120V go up to 15,000 BTU (above that, you’ll need 220/240V voltage). Obviously, dual hose units are better (higher efficiency, lower long-term costs; based on EER rating).

      3 14,000 BTU dual hose air conditioners will give you a combined cooling output of 42,000 BTU. That just might be sufficient given your in the northeast US; your calculations are again on point. You might want to check out our article about the best dual hose portable air conditioner here; you will find very efficient 12,000 BTU and 14,000 BTU units with a very good reputation.

      Overall, you do have a remarkably good eye for these BTU calculations and the general layout of portable AC units. You’ve got this solved.

      • I’ve been looking on at all of their various Mr. Cool DIY mini split configurations. My home is 100 years old, 8ft ceilings, mostly shaded except along the south facing side, located in Los Angeles. Our windows are all the original leaded glass french style, window a/c or portable a/c venting is not possible. The front public areas are an open floor plan, the living room is 40×23 and joins the 10×12 dining area thru an open double+ archway and has the 12×14 kitchen perpendicular. Dining area and kitchen along the sunny south wall. Would a 36k 16 SEER unit with the handler on the north LR wall alone be enough to cool the whole area, the full 50′ n/s width? Would we have a better cooling result if we place a 24k+9K, 24k+12k or a 18k+18k multi zone SEER 21.5 or 2 separate 18k SEER 20 units (for redundancy and no line extension cost) with the 9k, 12k or extra 18k handler on either the south dining area wall for cross ventilation or on the east dining area wall facing towards the kitchen?
        The 3 bedrooms, bathrooms and hall can be closed off by a door. The 23×12 master is at the end of an approx 75sq ft hall, I definitely want a unit in this room. Each bedroom to either side of the hall measures 13×13. Will a solo mini split unit in the center master cool the 2 side bedrooms at all? A 12k 22 SEER or a 18k 20 SEER is too big for that room alone unless the unit will actually reach to include cooling the 2 side bedrooms. An alternative option is the 27k 22 SEER 3 zone unit, with a 9k handler for each bedroom, likewise seems more than suggested for the per room sizes but is the lowest btu multi 3 zone unit. But it is true the home has no insulation and long thin glassed windows, perhaps higher btu are needed. What would you suggest?
        As I’ve never had a/c it’s hard for me to imagine one handler cooling several rooms, even with the appropriate btu’s for square footage, thank you for your help!

        • Hello Deborah, that was quite a read. You’re right; one air handler is not recommended, especially if you have bigger rooms far apart as in your situation. Two indoor units here are minimum; a 3-zone mini-split would be the most optimum option. One air handler in 40×23 living room, second in 23×12 master bedroom, and third either in the dining area or kitchen. You can check the best three-zone mini-split systems here; Senville units, for example, are both cheap and highly efficient. Total BTU output of 36k seems to be a good estimation.

          In any case, one air handler just can’t produce enough airflow for the air to reach all the rooms. If it would, that indoor unit would be ‘windy’ and noisy. Having 3-zone mini split, or even 3 individual 12,000 BTU Mr. Cool DIY units would be most optimal.

  38. How many BTU’s ASHRAE for 250 square feet, 8 ft ceiling, standard room, no sunlight or windows except for the AC vent, located in California?

    Also, do you know if the BTU rating affects dbA or sound level of a portable air conditioner?

    • Hello Annabelle, you’re looking for about a 6,000-7,000 BTU unit. Unfortunately, the smallest portable AC unit has 8,000 BTU ASHRAE.

      The source of sound in portable AC units is compressor and airflow. For higher BTU’s the compressor has to work harder and the airflow is higher; that’s why portable air conditioners with higher BTUs. You can see that very well in our article about the quietest portable air conditioners.

  39. Hi,

    I have a bit of a complex room I am looking to install a window ac unit and was hoping for some btu guidance.

    It is a 137 square foot bedroom with 8 foot ceilings. There is also an additional raised platform space that is about 4 feet high from the platform to the ceiling and is 135 inches wide and 27 inches deep.

    The building is a townhouse with 3 floors and the room is on the 3rd (top floor) and is directly under the roof which gets the hot sun of San Diego. The bedroom also has an attached bathroom and is the only thing on the top floor next to a very small hallway up a flight of stairs. This is also the only room in the house that will have an ac ( we are renters and that is nonnegotiable at the moment) and the house in general and especially that room gets quite hot in the summer.

    As far as I can tell, based on square footage alone I would be looking for a 5000 btu unit, but I am wondering if 6000 might be better given the location of the room and those additional factors. I definitely do not want to cause moisture issues by getting too big a unit, but do not want to undersize and have a unit not work either.

    Please let me know what advice you might have and thanks so much!

    • Hello there, you’re right, you have quite a complex situation and therefore the BTU estimate is not a piece of cake. 5,000 BTU unit might be adequate but with so many variables the safer option would be 6,000 BTU (San Diego, raised platform space, and so on). Hope this helps.

  40. Trying to figure out what I’d need for my enclosed patio. It has 2 (one exterior) doors, 6 windows, and 2 skylights. It’s 20ft by 15ft with 10 ft ceilings. There are 3 oaks but midday does get a lot of sun through the skylights. Live in Savannah, GA.

    • Hello Steven, patios are notoriously difficult to get a good BTU estimate. Let’s try this: the total square footage is 300 sq ft, and 10 ft ceilings. That’s about 10,000 BTUs estimate but those oaks are quite difficult to put into the equation. You can check out 10,000 BTU AC units here if it helps.

  41. Thank you for taking the time to answer these questions.

    I’m purchasing a Midea U window air conditioner to provide supplemental cooling for a hot bedroom in the summer. The bedroom is 17×18 with 9ft ceiling. The exterior wall faces west with 2 standard and 1 double window. There are doors to the bathroom and hallway but I keep them closed at night. I also keep the blinds drawn all the time but even still it gets hot from the afternoon sun and can be uncomfortable later for sleeping. I’m torn whether the 8000btu and 10000 btu units for my situation. The calculators seem to point to the 8000 btu unit being sufficient but I would love to hear your thoughts. I’m in Maryland

    • Hello Steve, the total square footage is 306 sq ft and you have an above-average 9 ft ceiling. For a standard room, 8,000 BTU could be enough. However, the west-facing wall, hot bedroom, and so on do indicate that you would need something a bit more powerful just to be safe. You’re doing the right thing with the blinds and keeping the door closed. If you’re looking at Midea U window AC unit (superb unit, by the way), it would be better to choose the 10,000 unit – the Midea U MAW10V1QWT here is perfect for your specific situation. Hope this helps.

      • It does help and thank you for the reply. I was thinking that the 10,000 unit was the better choice but then got worried about all the warnings about having a unit too big causes. The Midea looks like a really slick air conditioner. Thanks for your feedback on it. I’ve read a ton of reviews and can’t wait to get it installed.

  42. What a great website, I’m very impressed with how active the Q&A is. Thank you so much for doing this.

    I wanted to follow on from an earlier question where you advised the extra 4000BTU is not necessary if you are not an active user of the kitchen. I’m the same way and on balance would probably rather deal with the cooling maybe not being as effective for the 45 minutes every other day I am running my oven or using the stove, than step up the BTU and have higher energy usage the other 47 hours and 15 minutes.

    My question relates to how the kitchen bump up intersects with the common advice that if you oversize your unit, then it can lead to short cycles that leave you with humidity and wear out the equipment. No article online seems to makes clear how much wiggle room you have before that might happen, and often it’s simultaneously encouraged to go one higher than you need. Hence this 4000BTU kitchen bump comes to mind and whether that’s enough to amount to a harmful oversize during the majority time the kitchen is not used.

    I’m never quite sure if the spirit of the advice not to oversize is not to say install a 30,000BTU unit when you needed a 6,000BTU but perhaps there is much less harm if you install a 15,000BTU when you needed a 10,000BTU? Do you have any thoughts on what a safe buffer/range is if you’re trying to balance different operating scenarios?

    I have an open plan living room to an occasionally used kitchen, it’s a longer shape with a square footage a little under 300 sqft. There’s a door usually left open to a bedroom (about 110 sq ft and with its own A/C), and another to a <100 sq ft bathroom which can’t really be cooled except for whatever flows in from the living area. Ceilings are about 10’, and one wall is almost all windows – about 75sq ft of glass. It gets incredibly humid in the summer (90%+) but the windows are north facing and direct sun exposure is not excessive.

    There are different ways to cut this where I could calculate anything from 7,500 to 15,000 units, but am considering to go with a 12,000 unit on balance. Does this seem reasonable?

    Thank you so much!

    • Hello Aaron, that’s a very insightful comment. All your presumption about oversizing a unit, short cycles, wearing out, higher bills are on point. As well as pointing out that we don’t actually use the kitchen more than few hours per day maximum. The 4000 BTU addition for the kitchen is a result of EnergyStar’s recommendation; the justification for why 4000 BTU exactly is not all that clear.

      Oversize units and short cycles do happen if the unit is massively oversized (at least 50% but that’s a mere estimate). In your specific case, a 12,000 BTU or 14,000 BTU might be the safest option. Hope this helps a bit.

  43. hi,
    I have a 14Fx11F dining room 9F ceiling,
    open from 1 side to a small hallway, and from the other side to a small kitchen 11Fx8F, on the 4’th floor of a 6 floor apt. building, in NYC,
    what do I need?

    Thank you.

    • Hello Tar, you have a combined 242 sq ft space; with hallway, let’s round it up to 300 sq ft. Given the above-average ceiling height (9 ft), you should use 25 BTU per sq ft to be safe; that yields 7,500 BTU. For the kitchen, you should add an extra 4000 BTU due to high-temperature devices. Adding all up, you’re looking at 10,000 BTU or 12,000 BTU portable or window AC units. Hope this helps.

  44. We have a 540 sq. ft. seasonal cabin in central Minnesota with little insulation in the walls or above the 8 ft. ceilings. Casement windows are along the full wall in the living room and a sliding door in the kitchen – east exposure. Both bedrooms and bath (located between the two bedrooms) are west exposure with large double hung windows. The cabin is divided equally with open kitchen, dining and living room on one side. The center of this area leads to the other half of the cabin with both bedrooms and bath – west exposure. At the present time a mini-split a/c unit is not an option. Instead, we are considering an in-wall a/c unit centered on the east exposure wall between the living room and kitchen. With ceiling fans located in the living room/bedrooms and an additional fan strategically placed close to the bedroom area, we’re hoping to be able to move cool air to the back half of the cabin as well. Our temps in the summer can be in the upper 80s-90s with high humidity. With 540 sq. ft., we are close to the maximum for a 12,000 BTU unit. Based on our cabin size, layout and climate would a 14,000 BTU a/c unit be a better choice than 12,000 BTU?

    • Hello James, in-wall AC units are quite popular in the Northeast. Despite little insulation, this is still Minnesota. The addition of 4,000 BTU for the kitchen doesn’t really apply for a cabin kitchen, so the 12,000 BTU unit would most probably suffice. If you need some ideas, you can check our article about in-wall ACs. The #2 Frigidaire FFTA123WA1 in this article is a good option in this case. Hope this helps.

  45. Hi!

    I am looking to cool down a room that is 12x10ft with 9ft ceilings with one window that gets the sun in the morning, for two people sleeping and living in it. I might be able to buy a used 6,500 (DOE) BTU unit (10,000 ASHRAE) at a good price, but I was wondering if it would be too much for my room and would cause problems?

    Thank you so much for your input!

  46. Hi, Thanks for your website, you are a real life saver! I am living in hot and humid Montreal and I want to replace my old but still working window ACs with portable ACs. I am tired to install them (3) each year. One 5000 BTU in my bedroom 14X10 ft with 8 ft ceiling, window gets the sun in the afternoon. One in the living room 5000 BTU 13.75 X 9.5 morning sun (7 to 10) and one in the kitchen 6000 BTU 16X7 with full sun from noon to 6. I was thinking of a 5000 BTU in my bedroom and a second unit for the rest of the apt. 10000, 12000, 14000? I don’t know. I am afraid that with one unit only, my bedroom wiill not be cool enough and the living room will be like a freezer. Also , which brand is the quietest. What is the max DB I have to check to be sure it is quiet.
    Thank you so much for your input, very helpful.

    • Hello Monique, thank you for the question. The combined cooling output of 3 window ACs is 16,000 BTU; that should be your BTU target. Your thinking is on point; keep the 5,000 BTU window AC for the bedroom, and get a 12,000 BTU portable AC for the living room + kitchen. Noise-wise, the quietest portable ACs have the highest noise levels of below 55 dB. The perfect choice would be the overall quietest 12,000 BTU unit – the Frigidaire FHPH132AB1. We have an article about the quietest portable air conditioners here; the Frigidaire FHPH132AB1 is at #1 place because it’s the only one with below 50 dB noise levels (49 dB, to be exact). With 12,000 BTU, you don’t need to be afraid of insufficient bedroom cooling. The living room won’t be a freezer; even if you see that you’re getting too much cooling output, you can set the AC on a lower fan speed setting. Hope this helps.

  47. This comment section is fabulous to get feedback! Just want to get some validation on my situation, i’m ordering an air conditioner for my 1 bedroom (top floor) pre war south facing New York apartment with quite large windows. There is an open kitchen in the living area, i don’t do a lot of cooking, not sure whether to add the 4k btu or not?

    Main living room is 28ft x 11ft (50% of this has 10ft ceilings)

    Connected bedroom is 7ft by 20ft.

    I’ve been looking at a 10k BTU air conditioner, not sure if i’ll need 12k or it will be overkill.

    Thanks so much for running this thread!

    • Hello Anthony, thank you for your compliment; we do try to help everybody out. As far as your situation goes, the 4,000 BTU for the kitchen but you do have a refrigerator there; adding 1,000-2,000 BTU is reasonable. For the living room (308 sq ft, 9 ft average ceiling height), you would need about 7,000 BTU. For connected 140 sq ft bedroom, additional 3,000 BTU.
      All in all, 10,000 BTU could be barely enough; but 12,000 BTU is a much safer bet. You don’t have to worry about overkill here. If you find it useful, you can check out the best 12,000 BTU air conditioners here. Do keep in mind that if you choose a window AC unit, you have to – due to regulations in New York City – also have a support bracket for window AC units.

      • Thanks for this!! all in all if i include both rooms and bathroom and a more accurate calc it’s about 500sq ft mark with 9.5ft ceilings in 75% of the apartment, so i figure the 12k unit could work. Will there be a detriment if i go up one step more and go 14k BTU? Trying to work out what is overkill and what is not. Given it’ll be based on the below layout (which i’m definitely impressed on my keyboard architecture lol), i assume air will naturally flow a little into the bedroom with the fan, although not the best setup

        BedRoom (BR) is 170, Living Room with kitchen in it(LR) is 330sq ft
        Door-> ____|
        | |
        ______| |
        | |
        | BR | LR |
        | | |
        | | |

        • Now, those are some impressive keyboard skills! Never seems so astute a sketch with just a keyboard. If the combined 16,000 BTU was enough now, the combined 17,000 BTU (with 12k unit) should be enough. Of course, you can go with a 14k unit as well. It’s not exactly overkilled but it’s also not exactly necessary. Let’s say that summers might become a bit hotter in the next 10 years due to global warming; that would make 14k unit a sensible choice.

  48. We have a 2,000 sf home in the upper midwest. The first floor is about 1350 sf with 9 ft ceilings. The second floor is the other 650 sf with 8 ft ceilings. Our south facing windows are about 140 sf and north facing are about 111 sf. We also have an extra refrigerator and a freezer along with the usual appliances. We estimate we would need a 4 ton AC unit. We are wondering what you would estimate with this info. Thanks.

  49. Dear Sir,

    I have a complicated air conditioning situation. I live in southwest Missouri, with a hot, humid climate in the summer. The house, which I grew up in, is a one-and-a-half-story 1920s Craftsman-style house (not true Craftsman), with central air. Like my father, I keep the door at the bottom of the stairs closed to save on utilities. The upstairs consists of two bedrooms, which are divided by a hallway, which gives onto a stairwell from the gabled landing. The ceilings measure 7’3/4″ at their highest (in the two bedrooms, there are sloping ceilings on either side). The bedroom doors face each other, and the two windows in the south bedroom more or less face the single window in the north one.

    Here’s why it’s complicated. When my dad first put in central air in 1993, he bought me a Carrier Siesta II, 8,000 BTU unit (which has since literally disintegrated) for my bedroom (measuring about 179 sq. ft.). When my brother came to visit in the summer, it had to do for both bedrooms and the hall. I don’t sleep up there much anymore, but I used to run the Carrier to keep the upstairs at least dehumidified and not ungodly hot, partly because I have valuable tapes and books up on the hallway landing and in both bedrooms. There used to be enough cooling from the central HVAC system to cut the heat, as well; the new one (just installed through a Habitat program) doesn’t seem to be doing as well, though it reduces the humidity a little. (The former was a 2.5 ton Lennox, the new a 3-ton Goodman.)

    Given these this range of uses–one for the whole upstairs and one for the south bedroom only–do you think I need a unit with more than 10,000 BTUs? For several reasons, I’d rather not install a unit for each bedroom.

    I know this is a lot to ask you to advise me with, but I greatly appreciate your reply.

    • Hello Julie, sounds like a lovely house. We have two problems; hot air and humid air (those tapes and books can stand up the heat but not 50%+ humidity rates). If 8,000 BTU was not sufficient, the 10,000 BTU is the logical next step. Given that you have a problem with high humidity, a 12,000 BTU unit would be even better, however. Higher BTU units have higher dehumidification rates (measured in Pt/hr or ‘pints per hour’). Given your situation, a 12,000 BTU unit with the highest possible dehumidification rate would be the most optimum and adequate choice. Hope you find this helpful.

  50. Great article! But I am still doubting myself. Located in central California where we get some heat 90’s-100’s most of the summer. I have a 20×30 detached garage with 8′ ceilings. The ceiling and walls are insulated. The 12×7 garage door is insulated. There are (3) 4×4 Windows and (2) door standard entry doors. The building gets sun for most of the day. No stove or oven, but there are several arcade games and pinball machines that generate some heat, though not nearly as much as an oven. I was thinking a 24,000 btu single zone minisplit? Or would 18,000 be sufficient. Would like to keep the building at 70-72 in the summer.

    • Hello Mike, central California can get quite hot; you’re looking at 25 BTU or even 30 BTU per sq ft. The square footage is 600 sq ft; at 25 BTU per sq ft, you’re looking at 15,000 BTU units, and at 30 BTU per sq ft, you’re looking at 18,000 BTU units. Considering good insulation, 18,000 BTU should be sufficient. If you have some technical skills, you can choose the 18k Mr COOL DIY mini-split and install it yourself, for example.

  51. Thank you so much. I have my eye on that Mr Cool, but would really love the ceiling cassette. I think going for an 18k BTU unit would allow for me to go with a cassette size that would fit between trusses. Not completely DIY, but I can at least get everything done except the lines. This is wonderful information…Thank you!

  52. My central AC unit just went out in my 1,276 square foot house. I am unable to afford a new unit at this time and intend to buy window units for now. A BTU calculator says I need about 24,000 BTUS to cool this size house. My problem is, there is no way to put a window unit in the central living area. Would buying two 12,000 BTU units and placing them on opposite ends of the house do the same job to cool the entire area? Thank you for your time.

    • Hello Kris, this is an unfortunate situation. Regarding the total BTU cooling output, you’re correct: about 24,000 BTU should suffice. Central AC’s main advantage is the ductwork; it can easily homogeneously cool your entire house. With 2 window units, it depends on how easy/hard will it be for the airflow from both units to reach all parts of the 1,276 sq ft house. It might suffice; but the safer option would be to get three 10,000 units, for example. Sorry, this is truly a difficult situation.

  53. Hello, I live in Southern California my master bedroom is 15×20 with 9 foot ceilings it is connected to a master bath which is prob 120sqft my central ac does not cool
    Off my room enough. It has 4 windows in the bedroom 2 in the bathroom and has a lot of afternoon sun exposure. Should I go with 10,000btu or 13,000btu?

    • Hello Lindsay, it really depends on how much cooling output your central AC. In any case, the safer option is the 13,000 BTU unit; it will hardly be overkill, given only 3,000 BTU difference between 10,000 BTU and 13,000 BTU unit.

  54. Hello, I have a tiny 100 sq ft room in the garage that I am trying to turn into a hair salon. Do they make a mini split small enough for a/c and heat or what is my best option for that small of space? Thank you

  55. We built an enclosed porch at the back of our house. The ceiling is sloped from 8 1/2 up to 10 feet. It is 15 x 13. It has 4 windows and a glass door that face North. We live in Dallas, Texas. Is a 12,000 BTU window air conditioner to large?

    • Hello Tana, with porch air conditioners you have to increase the BTUs above 20 BTU per sq ft due to lack of isolation. Let’s presume the average ceiling height of 9 1/4 feet; that means that you should increase the BTUs per sq ft by 15% (standard calculation is made for 8 ft ceilings). For lower isolation, an addition of 20% would suffice. Dallas, Texas is a very hot place as well. Given all these considerations, 40 BTU per sq ft would not be too much cooling output.

      The combined square footage is about 200 sq ft. Even with 40 BTU per sq ft, you’re still looking at 8,000 BTU. 12,000 BTU would be overkill. The reasonably safe bet would be 10,000 BTU. You can check some of the 10,000 BTU window air conditioners here (hope you find it helpful).

  56. Would a 14,000 btu window unit be adequate for an added on den (no windows-only a skylight) that has insulated walls but not roof, 24×14, morning sun exposure, adjacent to kitchen, very hot in Louisiana ! Thanks much ! Look forward to hearing from you soon.

    • Hello Marlene, we’re talking about a 336 sq ft space. If it were a normal room in an average climate, you would need about 8,000 BTU minimum to cool it sufficiently. Add hot Louisiane, sun exposure, and so on, and you get to as much as 14,000 BTU. In short, 14,000 BTU is adequate AC sizing in your situation.

  57. I have a 30′ x 30′ garage with 10″ high walls and no ceiling, it’s fully insulated (6″ fiberglass roll), I guestimate that 30,000 BTU mini split would work, but would appreciate your input, please. I live in Southeast CO and it can get hot here, but not usually anything above 107F in Spring/Summer/Fall. Also it can get below 0F in winter, and I wonder about Heat Pump efficiency at those low temperatures, for Winter heating.

    • Hello Jim, that’s a 900 sq ft area with 25% higher-than-usual walls. If you use the 20 BTU per sq ft rule and add that 25%, you get 22,500 BTU capacity. Let’s say 24,000 BTU or 2-ton heat pump, given it’s Southeast CO. For winter heating, you need to check the HSPF rating (HSPF4, to be exact). It should be at least 9, anything above that is great. The best 24,000 BTU heat pump is the Air-Con ABXCI4H4S24/ABXEM4H4S24; you can check out our article about the best mini-split heat pumps here (the Air-Con unit actually has the #1 rank). Hope this helps.

  58. Hi.. I love your article and comments.

    Would a 8,000 or 9,500 BTU window air conditioner for a 16×12 bedroom with 12 down to 8 foot sloping ceiling be adequate? This room faces the south, has 2 windows and is also on the 2nd floor. Attached is a master bath with 1 window and a walk in closet with another window. Doors are mainly closed.

    • Hello Bob, thank you. With the doors leading to the master bathroom and walk-in closet, we’re looking at roughly 200 sq ft with 10 ft average ceiling height. If we apply the 20 BTU per sq ft of living space (8 ft ceiling) rule, you could get away with as little as 5,000 BTU. However, the 8,000 BTU cooling output is a much safer and appropriate choice; 9,500 BTU would be a bit of overkill. For the bedroom, you’re probably looking for a window unit that is as quiet as possible; maybe our article about the quiet window air conditioners here can help you narrow down the choice of the specific unit.

  59. Hi,

    I have a 8×12 ft. room with 2 walls 4 ft. tall and the rest slanted (highest height is a little over 7 ft.) It gets very hot in the summer. (In NJ)
    What would you recommend?

    • Hello Tova, you will need the smallest air conditioner on the market. The absolute smallest units are 5,000 BTU window AC units. You should check our article about small AC units here; the hOmeLabs 5,000 BTU window AC will be more than enough for your situation.

  60. Hi there!

    My bedroom measures 155 sqft, 8ft ceiling, it is South Westerly facing, so it has sun from around 10:00 until it sets and a large window measuring 6 ft x 4 ft.

    I am looking for a portable air conditioner, which will be vented through the wall and I have used various BTU calculators that suggest 5000 BTU. Adding 10% for the direction of the bedroom gives 5500 BTU, so 6000 BTU but these are few and far between, so I am looking at 7000 BTU.

    My issue is I like to do a lot of research and many of the user reviews of 7000 BTU units, which are technically more powerful than needed, include room dimensions similar to my own but complain about the AC struggling in warm to hot weather. I have read the same even of 8000 & 9000 BTU units with similar room dimensions.

    I am confused as the advice is not to go too large due to the larger machines inadequate dehumidification in smaller rooms.

    Can you please offer any advice as I obviously don’t want to purchase something that’s absolutely on its limit all summer, despite being more powerful than I need on paper, but neither do I want to oversize even more and find I have a cold but humid bedroom?

    Very informative website!
    Thank you.

    • Hello Stefano, it’s really nice to see your thought process; very accurate and on point. You pretty much know that 6,000 BTU will be sufficient but the smallest portable AC unit has an 8,000 BTU cooling output. So, you’re stuck with picking an 8,000 BTU unit, and the dehumidification (AC short-cycling) is exactly the right concern.

      Now, the key question is how much bigger AC unit can I buy and still avoid ‘cold but humid’ conditions due to oversized AC. Truth be told, that’s really hard to show for sure. The rough consensus (a rule of thumb if you will) is that AC shouldn’t have 30-40% surplus cooling output. Example: If you need a 10,000 BTU unit, buying a 14,000 BTU unit is a bad idea (you will have humidity problems).

      In your case, you have a smaller room and the calculations are hence less exact here. 8,000 BTU unit will have a 33% surplus cooling capacity if provides 6,000 BTU sufficient cooling. It’s right there on the limit.

      Our suggestion is this: Get the 8,000 BTU unit. It’s the smallest portable AC you can buy. Best case scenario: You will have an adequately cold and dehumidified bedroom, chances for this happening are considerable. Worst case scenario: You will have an adequately cold yet humid bedroom. At this cooling capacity, that’s less likely to happen. In either case, the lack of dehumidification, if it occurs, would be minimal.

      Hope this helps.

  61. Thank you so much for taking the time to read my my rather long winded message and for your very detailed reply.

    It is all too easy to focus on those more powerful conditioners as they cost very little more and tend to have additional features missing from the lower powered models such as Auto fan and remotes with inbuilt thermostats (I like gadgets).

    You have confirmed what I suspected and that’s to size the air conditioner as accurately as possible but with allowance for the variables you mentioned. I shall start my research of the 8,000 BTU units and I will report back on my findings.

    Thank you once again for your very kind advice.

  62. Good Evening. I want to start by thanking you for all of the time you have taken to help so many of us as we struggle to find the right size unit to cool our homes and keep our sanity in check. Not to mention the money factor. Again, a HUGE Thank You. As to my set-up. I live in upstate NY. My 3-season room is 24×16 with a cathedral ceiling. The height of the wall before it starts its slope upwards is 13’. The height at the apex is about 17’ to 18’. One ceiling fan, 2 skylights. 3 of the walls are exterior facing. The first 16’ exterior wall has 2 standard 72”(w)x80”(h) sliding patio doors. A lot of late morning thru late afternoon sun pours on this side of the house. This side is my trouble spot. I have heavy curtains covering the sliding doors but the heat still makes its way into the room. The opposite 16’ exterior wall has a standard 32”(w)x80”(h) door plus a casement window 70”(w)x 60”(h). No sun hits this side of the house. The remaining exterior 24’ wall is primarily all windows; 20’ of window expanse plus windows in the triangular section of the wall created by the slant of the cathedral ceiling. This 20’ is comprised of 4 casement windows all 60” in height. This side has no direct sun at any point due to shade trees. The last 24’ wall is interior, has one standard sliding 72”x80” door plus two 36”(w)x48”(h) windows. The skylights appear to be standard in size but do let a lot of heat in when the sun is directly overhead. I hope to put something in place to block some of the sun from entering these skylights. Overall, the 3 season room has about 5 or 6 hours of direct sun. The square footage of the room is 384 but grossly underestimates the required BTU to cool this room. My thought is that I need either a 14,000 BTU unit or an 18,000 unit. Given all the specs provided, what recommendation would you suggest? On a side note, I picked up a Frigidaire 14,000 BTU portable A/C but so far it doesn’t seem to be up for the challenge. Although the room is cooling down to it’s 72 degree setting, the room feels muggy and not cool like the rest of the house which is cooled via central air and a temp setting also at 72. Thank you in advance and my apologies for the length of this write-up.

    • Hello Robert, thank you for very much your comment (it means a lot) and sorry for the comment error, we’re trying to fix it. That’s a very detailed description containing a lot of important factors. Let’s simply it: average 384 sq ft room with an 8 ft ceiling would require 384 sq ft * 20 BTU per sq ft = 7,680 BTU. However, your ceiling is, on average, 15 1/4 ft high. That means that you have 91% more air in your square footage than a room with an average 8 ft ceiling height; we get to 14,640 BTU.

      Now, you do have a bit over-average sun exposure. The 14,000 BTU not adequately cooling your room does make a bit of sense. You would require at least 15,000 BTU, up to about 20,000 BTU of cooling output. How much exactly it’s really difficult to pinpoint. 18,000 BTU would be a safe choice but the biggest portable AC units go only up to 14,000-15,000 BTU. Options for 18,000 BTU are a mini-split or a bigger window AC unit. You do find yourself is a bit of a struggle here but hopefully, you can resolve it. The 14,000 BTU unit is undersized by a few 1,000 BTUs. Hope this helps.

  63. I’m building a new home in Ft Myers Fl. The new house will have a 4 car garage – 1630 sq ft. The garage is on the North side of the house. There are windows in the garage doors but they face Northwest. The interior height of the garage is 12ft. I am having the builder insulate the garage during construction but they are not installing AC ducting for garage.

    I will be away from this home during the hot summer months however I will have vehicles in the garage during the summer months. I would like to keep the vehicles as rust free as possible and therefore am exploring AC options for the garage. I’m not looking to keep the garage at normal household temps. Just conditioned enough to keep humidity down in the garage. Maybe set at 80 degrees??

    I’m planning to install AC AFTER the home construction is completed. Should I use the larger 36,000BTU unit or consider 2 smaller units? Thanks

    • Hello Peter, you’re right, the combination of high humidity and high temperatures is ideal rust-formation. Humidity is the more serious concern here; it would be smart to start with a smaller BTU output (2 smaller units) and see how they lower the relative humidity levels. If they don’t fall below 60%, you could buy an additional AC unit but a better option would be a dehumidifier. A dehumidifier won’t lower the temperature but will be very effective at lowering the relative humidity levels. It’s really hard to estimate exact BTU requirements in this case.


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