MrCOOL DIY Mini Split Reviews: Exactly How Good They Are? (2022)

There is nothing like the new Mr COOL DIY mini split series. While the big companies stopped innovating a decade ago, Mr COOL is literally a breath of fresh air of innovation in the HVAC industry. We will review Mr COOL mini-split systems; the trendsetter air conditioning/heat pump systems.

Here is the quick outtake of the 3rd generation 12k, 18k, and 24k Mr COOL mini splits:

  • They have a high 20+ SEER rating and 10 HSPF rating (incredibly energy-efficient).
  • They are modernized; modern design, mobile app integration, great appeal.
  • Most importantly, you can DIY the installation.

Here’s the deal:

Installation of a mini-split unit averages at about $3,000.

If you can avoid that cost, you obviously should. Before Mr COOL, only the incredibly technical people managed to DIY a mini-split (barely). With the Mr COOL mini-splits, you get an incredibly efficient, easy-to-install device.

Note: As always, if you have any problems selecting the size of MrCool, or with the DIY installation, you can use the comment section below and we will help you. Currently, we have more than 90 comments, solving almost 50 MrCool related questions.

Here are two conditions to avoid that $3,000 installation cost:

  1. Be just a bit of a technical person (we’re not talking rocket science; basic DIY skills will do).
  2. Buy the Mr COOL DIY unit of appropriate capacity (you have to choose between 12k, 18k, 24k, 36k models – more on that later on).

Mr COOL DIY 3rd generation mini-split units don’t need professional installation. In this Mr COOL mini split review, we will look at 12k, 18k, 24k, and 36k systems.

Here is an interesting part:

All Mr COOL mini splits are the future of air conditioning/heating. However, many people are shocked to find out that some Mr COOL models are better than others.

What really mind-boggles some people is why is the smaller 12k unit more expensive than the bigger 18k and even 24k unit. We’ll explain in detail why the 12,000 BTU Mr COOL is such a smart investment.

Let’s first look at the comparison of the Mr COOL DIY mini-split. After that, we’ll explain which device is the best for a certain area and look into the energy-efficiency (the most important factor when buying any mini-split heat pump). We will also review each Mr COOL mini-split system (below the comparison table).

Comparison of Mr COOL DIY Mini Split System

MrCOOL Comparison: Mr COOL DIY 12k Mr COOL DIY 18k Mr COOL DIY 24k Mr COOL DIY 36k
Photo: DIY-12-HP-115B
mr cool diy 36k
Recommended Area: 500 Sq Ft 750 Sq Ft 1000 Sq Ft 1500 Sq Ft
Cooling Output: 12,000 BTU 18,000 BTU 23,000 BTU 34,500 BTU
Heating Output: 12,000 BTU 18,000 BTU 25,000 BTU 36,000 BTU
SEER Rating: 22.0 SEER 20.0 SEER 20.0 SEER 20.0 SEER
HSPF Rating:  10.0 HSPF 10.0 HSPF 10.0 HSPF 10.0 HSPF
Voltage:  115 Volts 230 Volts 230 Volts 230 Volts
Average Rating: 4.9 out of 5 stars 4.7 out of 5 stars 4.7 out of 5 stars 3.9 out of 5 stars
Availability: Check Price Check Price Check Price Check Price

Which Mr COOL Mini Split To Choose (Based On Square Footage, Energy Efficiency)

As you can see, Mr COOL makes mini-split with different cooling/heating capacity (measured in BTU; British Thermal Units).

It’s important not to pick a mini-split that’s too big or too small for your needs.

Appropriately sizing a mini-split will lead you to either lower energy-efficiency (can cost $100s/year in electricity costs) or limit the lifespan of the device. Therefore you need to take into account the recommended areas for each Mr COOL DIY mini-split.

What size MR COOL do you need?

Here’s how big a MR COOL you need (coverage areas):

  • For 500 sq. ft., choose the 12,000 BTU Mr COOL.
  • For 750 sq. ft., choose the 18,000 BTU Mr COOL.
  • For 1,000 sq. ft., choose the 24,000 BTU Mr COOL.
  • For 1,500 sq. ft., choose the 36,000 BTU Mr COOL.

If you’re somewhere between these recommended areas, you can give us your situation in the comments below or use our BTU calculator here.

Now, let’s look at the most important aspect of every mini-split system:

Energy-Efficiency (SEER And HSPF Rating)

Surprise: When you compare the prices of 12k. vs 18k. vs 24k Mr COOL DIY systems, you might notice that the smallest one (12k) has the same (or even higher) price tag as bigger 18k and 24k units. Energy-efficiency is the key here:

The whole point of buying an efficient Mr COOL mini-split is to reduce future electricity costs. Here we need to look at the specifications:

  • SEER rating (cooling). Industry-standard is 14-16 SEER rating (Mr COOL have 20 SEER rating).
  • HSPF rating (heating). Industry-standard is 8-9 HSPF rating (Mr COOL have 10 HSPF rating).

Based on these ratings, we can determine that Mr COOL mini-split units are any good; in fact, they are exceptional.

Some units are better than others. Here is how we can rank the Mr COOL mini-split systems:

  • 1st Place: 12,000 BTU unit with 22 SEER and 10 HSPF rating.
  • 2nd Place: 18,000 BTU and 24,000 BTU units with 20 SEER and 10 HSPF rating.
  • 3rd Place: 36,000 BTU unit with 16 SEER and 8.9 HSPF rating.

As you can see, the 12k Mr COOL DIY can command a higher price just because of its 22 SEER rating. That means that the 12k unit is about 10% energy-efficient than 18k and 24k. How does that translate into electricity dollars?

Simple: If the seasonal electricity bill for Mr COOL air conditioning is $1,000 for 18k and 24k unit, it will be only $900 for the 12k unit. Essentially:

Extremely efficient 12k Mr COOL can save you $100/year in electricity cost compared to 18k and 24k unit. In 10 years, that’s $1,000.

This is the very reason why the 12k unit can have the same or even higher unit cost compared to 18k and 24k device.

On the other hand, if you look at the SEER and HSPF rating of the 36k unit, you can see that the energy-efficient is not as splendid as the smaller Mr COOL mini-split units. You can find a better 36k unit; however, you won’t find a better 12k, 18k, or 24k unit.

That’s why we’ll review each of the best Mr COOL air conditioners – the 12k, 18k, and 24k.

Mr COOL DIY 12k Review

SEER Rating (Cooling): 22
HSPF Rating (Heating): 10
Cooling Capacity: 12,000 BTU
Heating Capacity: 12,000 BTU
Voltage: 115V
Rating: 4.9 out of 5 stars

The 12k unit by Mr COOL DIY is just remarkable in many aspects. Apart from superb energy-efficiency, it’s a highly modernized mini-split system; the likes you won’t yet see from even the biggest brands such as Mitsubishi or Fujitsu.

One key feature is the new SmartHVAC app. Standard mini-splits are controlled via a remote controller. The Mr COOL 12k can be controlled via iPhone or any Android phone. You don’t even have to leave the couch; increase or decrease the temperature with the scroll.

Of course, we can’t overestimate how essential the energy-efficiency is. In fact, the 12k model is the best mini-split in 2020 purely due to the 22 SEER rating. Its cooling effectiveness is 10% higher than most other mini-split units, including the Mr COOL 18k and 24k units. Add the HSPF heating rating, and you have an eco-friendly mini-split that will last for 15+ years.

The vital ingredient for such high efficiency is the variable-speed DC inverter compressor. This alone can cut the yearly cooling/heating costs by several $100.

The DIY process is easy: you get a pre-charged R-410A 25 quick connect line. You will be able to install the Mr COOL 12k without any specialized tools professional installers use.

On top of that, the 12k is the only Mr COOL DIY unit that runs on 115V. That means you don’t need any electrical work; you have low voltage and low amperage.

All in all, the 12k is the modern trendsetting air conditioner/heat pump. This is the future of all mini-splits.


  • Unbeatable 22 SEER rating with 10 HSPF rating
  • Only Mr COOL DIY unit that runs on 115V (even easier installation)
  • DIY installation saves you about $3,000
  • Affordable price given the low electricity costs you can expect in the next decade or two
  • Only for 500-600 sq. ft. spaces or smaller

Mr COOL DIY 18k Review

SEER Rating (Cooling): 20
HSPF Rating (Heating): 10
Cooling Capacity: 18,000 BTU
Heating Capacity: 18,000 BTU
Voltage: 230V
Rating: 4.7 out of 5 stars

18k units are very popular. You’ll rarely find 20 SEER, 10 HSPF rating mini split; that’s exactly what the Mr COOL 18k offers.

It has a DC-inverter compressor that is quiet and enables such high energy-efficiency.

What is more, it can cool down or heat places that are about 750 sq. ft. big. That means that it will fit well in big living rooms and bedrooms.

You also have all the modernization; not does the 18k have an inverter compressor, you can also use the SmartHVAC app to control it, and it has a modern design. That’s much more appealing than the classic mini-split heat pumps.


  • High 20 SEER and 10 HSPF
  • Can cooling/heat spaces around 750 sq. ft. big (1 big room, or 2 small ones)
  • Low price given the 18,000 BTU of power
  • Needs 230V voltage
  • Combined weight is 222 lbs, you’ll need strong arms for DIY installation

Mr COOL DIY 24k Review

SEER Rating (Cooling): 20
HSPF Rating (Heating): 10
Cooling Capacity: 23,000 BTU
Heating Capacity: 25,000 BTU
Voltage: 230V
Rating: 4.7 out of 5 stars

24k unit is the biggest Mr COOL unit that has a 20 SEER rating. You will also notice a bit of discrepancy as far as the cooling and heating capacity is concerned; the cooling capacity is 23,000 BTU and the heating capacity is 25,000 BTU.

This is the most popular big 1 zone mini-split unit. That means that you can use it to cool/heat the entire flat or several rooms. The total recommended area of use is 1,000 sq ft.

It’s quite an achievement that the 20 SEER (and 10 HSPF) can be achieved; higher capacity mini-splits usually have much lower energy efficiency.

All in all, if you need a bigger Mr COOL mini-split, this is the right choice. Needless to say, you will be able to DIY the installation and save yourself $3,000 installation cost.


  • Innovative big 24,000 BTU Mr COOL air conditioner
  • Managed to keep the high 20 SEER rating
  • Very quiet heat pump with low noise levels (like all Mr COOL units)
  • Can handle about 1,000 sq. ft. of space (entire flat, or several rooms)
  • Affordable price (below $2,000) for such a big device
  • Installation is a bit tougher due to a larger device
  • You will need 230V (but no amp breakers in most cases)

Verdict On Mr COOL

Undoubtely, the Mr COOL DIY mini-split units are the way of the future. The innovation is seen everywhere; from the design, DC inverter compressor, and WiFi connectivity to the SmartHVAC app.

In the future, we’re likely to see other companies following the Mr COOL footsteps. However, as of now, nobody has managed to snatch the holy grail of mini-splits:

To create a mini-split that everybody could DIY with ease.

With Mr COOL, you will not only save yourself the high installation costs, but due to high energy-efficiency, you will see your cooling/heating electricity bill reduced by several $100 per year.

99 thoughts on “MrCOOL DIY Mini Split Reviews: Exactly How Good They Are? (2022)”

  1. My house is a two floor semi with a basement. The stairs are on the outside wall of the house. The building is 29.5 x 19.7 irr ft. The upstairs is about 500ish sq ft and the main floor is the same. Does this make the area to cool about 1000 sq ft?
    I intend to buy a MrCool and install it at the top of the stairs on the 2nd floor. I am guessing that by doing this I will be able to cool both the top and main floors. Is this correct? Which MrCool should I buy?

    • Hello George, two-floor houses usually required 2 units. If you go with the bigger 24k unit, it could (in theory) cool both floors, if you just look at the square footage. However, the distribution of air from a single unit can hardly cover 2-floors. Cool air does have a higher density than hot air, and 2nd story unit cold provides a cooling effect to the 1st floor because cool air will be dissipated in the lower floor. Unfortunately, that will probably not be enough.

      For your situation, you would require 2 units; the most optimum would be 2x 12k MrCOOL units here. 1 unit for the 1st 500 sq ft floor and the second for the 2nd 500 sq ft floor. The added advantage here is that you will need less airflow to cool both places; this translated into a quieter operation. 12k MrCool is the quietest unit with 38/31.5/23.5 dB indoor noise levels for high/mid/low fan speed setting; other units generate well over 40 dB noise levels. Hope this helps.

      • Hello, I also have similar setup. 1000 Sq ft condo. 500sq ft upstairs with 2 bedrooms. And 1 larger 500 Sq ft room downstairs. Would it be better to get 2 12k units? Or 1 18btu or 24btu with multiple zo es. Wouldn’t having two 12k units one upstairs and one downstairs be more on energy bills?

        • Hello Matt, in this situation, 2 units would be better. Yes, you will have lower energy bills but 2 12k cost more than 1 18k unit. That’s the compromise here.

          • Do the 12k btu units need to be hardwired, or do they have a plug, and can simply be plugged in. My electrician is quoting $900 dollars to put in 220 outlet, because of its location, and he said would cost the same for 115v. So, if the necessary electrical requirements cost the same, is it still better to get 2 units? Or maybe one unit with multiple(3) zones. Also, in the multiple zones is it possible to get different btu ratings on the air handlers?

          • Hello Matt, all mini splits have to be installed (all that hole through the wall thing). They do need to be hardwired but we usually have 115V circuits and you don’t need an upgrade; that is a specific advantage of 12k Mr Cool units (bigger units require an upgraded 230V circuit). 115V outlet shouldn’t cost as much as a 220V outlet since you don’t really need to upgrade the circuit; you just use the existing circuit.
            If you get 2 units and pay the same as for 1 unit, it makes sense to get 2, of course.
            With multi-zone mini splits, you can get 6,000 BTU, 9,000 BTU, 12,000 BTU, 15,000 BTU air handlers and so on. You can get the combination. To get an idea of what these 3-zone units look like, you can consult these 3-zone mini split units. #5 Mitsubishi MXZ3C24NA2U1, for example, has one 6k, one 9k, and one 12k air handler. Hope this helps.

  2. Hi. I’m interested in your DIY Single Zone unit. It’s going into a 22′ X 22′ garage shop with 9.5 foot ceilings. That’s about 484 square feet, but I have a 16 foot garage door to contend with for possible air infiltration. The ceiling is insulated and I’m planning on insulating the walls. I’m in Virginia Beach, so temperatures range from a high of about 105 in summer to 15 in the winter. I’m also already wired outside for a 220V disconnect, so I think the ton and a half unit (18K) is what I need.

    My primary question is whether shorter supply lines are available? It looks like the standard package is a 16 foot line. I’m planning to run the lines inside the wall between the studs to the outside and I’m estimating at most a 9 to 10 foot run. I would prefer not to have a 6-7 foot coil of gas line on the exterior of the house.

    • Hello Scott, your BTU estimate checks out. The 16-foot line is the standard length, and it’s really difficult to use a different one. Usually, you could buy an additional 10 ft supply line but the whole point of Mr COOL DIY units is that you get everything in the box (standard measures). If you’re a bit crafty, you could try to hide that 6 ft of the line you don’t need inside the walls. Running it on the exterior of the house doesn’t really look aesthetic, you’re right.

  3. I have a 2000 square foot spray foam insulated shop. 300 square feet is office space and the remaining 1700 is open shop space. Would like to have 2 interior units so when cooling or heating the shop area isn’t needed I can cool or heat the office only. What size btu unit do you recommend?

    • Hello Marc, let’s presume the shop and the office have 8 ft ceiling. The combined square footage (2000 sq ft) would require a minimum of 40,000 BTU cooling/heating output. 2 x 24,000 BTU Mr COOL units should do the job very well. The specific serial number of units is DIY-24-HP-230B and you can check them here. The recommended coverage area is exactly 1,000 sq ft; so for shop + office you just install 2 units.

  4. Standard mini-splits are controlled via a remote controller. The Mr COOL 12k can be controlled via iPhone or any Android phone. You don’t even have to leave the couch; increase or decrease the temperature with the scroll.

  5. Hello, I live in Kentucky and have hot and humid weather. I have a 1600 square foot shop with 12 foot ceilings. The building is insulated very well. Would the 36k btu mr. cool unit be enough to cool my building. Thanks!

    • Hello Logan, the DOE’s rule of thumb states ’20 BTU per sq ft if you have 8 ft ceiling’. You have 12 ft ceiling; so let’s say you would need at least 30 BTU per sq ft. 1600 sq ft * 30 BTU per sq ft = 48,000 BTU. Hence, in your situation, the 36,000 BTU Mr COOL would not be sufficient. The better and more adequate solution would be two 24k Mr COOL units with a combined cooling output of 48,000 BTU. Hope this helps.

  6. I have a modular ranch house built 1984, approximately 1000 sq ft. The living room, dining room and kitchen are all one room with a 1/2 vaulted ceiling in the dinning room/living room combination and a 8 ft ceiling in the kitchen. I also have afi used basement with a one car garage underneath. This is an all electric house. I put in a propane stove in the living/dining room for heat in the winter. 2 bedrooms and bath, all on one floor. How many mini splits should I buy as I want to use it for heat and air conditioning?

    • Hello Barbara, for a 1000 sq ft ranch house you would need a total cooling output of about 20,000 BTU. But this is a modular house with several rooms; you will need 2 air handlers to homogeneously cool and heat the house. If you go with Mr Cool, the most optimum option are two Mr COOL DIY 12k units; 1st air handler should be in the living room and the 2nd one in the kitchen.

  7. Hello,
    I’m planning on buying the 12K DIY Model and want to run it on my solar (3kW) with a battery bank of 12,000 W hours. Right now, I have a through the wall 12,000 BTU just A/C and when I plugged it in to Solar, for some reason my voltage kept dropping on my inverter, So I can’t run it off Solar. With this one, could I splice an extension cord onto the electrical leads and either plug it into the electric company or my solar? I believe this one will work with Solar because it has a lot lower amperage (2.5A) and would only use about 300W on low. How many Watts does the medium setting use? Thanks.

    • Hello Bill, the dropping voltage is concerning. Usually the voltage remains the same, and amps and watts change. Splicing extension cord might work; it’s really hard to know for sure, however. 12K DIY model has max. wattage of 960W (based on 12.5 EER rating) and max. cooling amperage of 15A. 300W is a bit low; at 300W, you would be getting about 3,750 BTU cooling output. The medium setting still has 500W+ wattage and requires at least 5 amps. Hope this helps a bit.

  8. I have a two story house – 4 bedroom upstairs about 1,250 sq feet, downstairs about 1,100. Would the 36k mini-split with 4 zone attachments work fine for this?

    SoCal by the beach so would use in the hot august/September months but rarely above 80-85.

    • Hello Chris, for a combined 2,350 sq ft, you would require 47,000 BTU unit, given the ’20 BTU per sq ft’ rule of thumb. 36k unit might even be enough; you can always get an additional 14,000 BTU portable unit, for example, if you find the air conditioning insufficient.

  9. I ordered a 36000 btu diy mr cool unit the other day but I was going to put it on a 30 amp breaker. Now I’m seeing I might need a 40 amp breaker? Does this mean I can run it at half power or something like that? Thanks in advance if anybody as some answers

    • Hello Colin, this question would be best answered by Mr Cool guys. We can theorize a bit here but they have the practical measurements and will give you the clearest and most realistic answer.

  10. I have a shed that i insulated that is 12foot x 16foot and the total height is 12 feet. I live in the dallas/ft.worth area and can get quite hot. What is the recommended unit size i need for such intense texas heat?

    • Hello Bill, 12×16 is combined square footage of 192 sq ft. For 8 ft ceilings and standard climate, you should use the ’20 BTU per sq ft’ rule of thumb. With a 50% higher ceiling (12 ft), that’s about 30 BTU per sq ft. Factor in the intense Texas heat, and you’re looking at 40-45 BTU per sq ft. At 45, you’re looking at 8,640 BTU; 10,000 BTU to be safe. That said, the Mr Cool 12k BTU would not be overkill. You just run it on a lower speed setting for optimum cooling capacity output.

    • Hello Patrick, all air conditioners have a dehumidifier built-in. With Mr Cool units (12,000 BTU) included, you can even set them into ‘Dehumidifier mode’.

  11. Hello- what is the maximum run allowed to connect the indoor and outdoor units? We knocked down a bunch of walls to make our first floor open concept and added windows. So now the only wall space I have to permanently mount the indoor air handler is on an exterior wall but against my attached garage. So we would have to run the supply lines through the garage to the exterior unit. It would be 23.5 feet just to reach the outdoors, then down from there to reach the unit on the ground. Is this length prohibitive for mini splits?

    • Hello Christina, the max. length is 25 feet. The standard length is 16 feet; Mr Cool units have an above-average refrigerant line length. Now, having knocked down a bunch of walls and having 23.5 feet just to reach the outdoor is quite an uncomfortable situation to be in. You’re only left with 1.5 feet to reach the unit on the ground; which probably won’t be enough. We are sadly not aware of any mini-split with 25+ feet refrigerant lines. Hope you find this at least a bit helpful.

      • Mr Cool offers a coupler and allows several linesets to be connected. I see appliance connection offers a 75′ precharged line.
        Can’t remember what the manual says but max distance is pretty far.

  12. Hello, We have a 1400 sq ft home in CT. 700 sq ft are a great room with a 9 ft cathedral (kitchen, living and dining room). 700 sq ft are 3 bedrooms, 2 bath and a hallway. We want to DIY install 2 Mr. Cool mini-splits, 1 18,000 btu unit in he great room and 1 12,000 btu unit in the bedroom (13 x 13) that is at the end of the hallway and faces the great room. Are these the correct units to buy or do you suggest another size? We want to make sure we do this correctly, soany and all info is appreciated. Thanks

    • Hello Mary, you’re correct, it’s best to make sure your BTUs are adequate for the size of your home. It’s usually recommended to use the ’20 BTU per sq ft’ rule of thumb with these calculations. The 18,000 BTU unit for the great room (700 sq ft) would be sufficient; you’re lookt at about 25 BTUs per sq ft.

      The 2nd unit (in the bedroom) should be larger. Correct me if I’m wrong, but it should cool down combined square footage of 700 sq ft? 12,000 BTU unit won’t suffice for 700 sq ft, unfortunately. 18,000 BTU would be a better choice. Hope this helps a bit.

  13. Is a 12K unit to much for a 12 x 16 outdoor office studio unit with a pitched roof goes from 8′-9′
    As Mr. Cool does not offer a 9K in the DIY product line, if a 12K it is to much for this space which other MR. cook product do you need. Living in Northern California I need an energy efficient unit with low amps.

    • Hello Audra, for a 12 x 16 office studio the 12k unit might be overkill. Now, you can get the 12k unit and run it at low speed. The main thing you have to worry about oversized air conditioners is the short cycling (AC turns on and off repeatedly with high frequency). Given Northern California can be quite hot, you most probably won’t have this problem even with the 12k unit.

  14. I have a log cabin in western Wisconsin it has a 30 x 30 foundation and is 26 feet to the peak. It also has a 15 x 30 loft and a 15 x 10 bed room on the main floor. What would you recommend. I’m only looking to get another month in the fall and one in the spring of use. This, other than a fireplace would be out only heat source.
    The roof is very well insulated, good windows and doors and the walls ate 8 in thick.

    • Hello John, first you need to get an idea of how many heating BTU you need. You can consult the heating BTU map here; you’re probably in Climate Zone 6 and would need about 55 BTU per sq ft (8 ft ceiling) for adequate heating during the winter. You will also require the total square footage; bedroom and loft combined are 600 sq ft. Now, the ceiling is probably higher than 8 sq ft; let’s presume that the average ceiling height is about 12-14 ft; you will need to use 80 BTU/sq ft in the calculations in this case.

      600 sq ft * 80 BTU/sq ft would be about 48,000 BTU. Fireplace + MrCool heat pump should provide about that kind of heating output; maybe a bit lower due to good insulation your log cabin has. The biggest Mr COOL DIY 36k would be, given these presumptions, a good choice because it generates 36,000 BTU of heating output. The fireplace heating output may vary but most fireplaces (at least 1,5000W electric ones) have a 5,000 BTU heating output. Hopefully this will help you a bit.

  15. Hi, I have a 1500 sqft home that is L shaped. One end is bedrooms the other end is family room that is open and goes straight into the kitchen.

    I was wondering what you would recommend. Can I get by with 1 units like a 24 or 36btu? Or should I break it into 2 units?

    Thank you for your help.

    • Hello Micah, if you apply the 20 BTU per sq ft rule of thumb, you would need about 30,000 BTU of cooling output. Now, you can get a 36k unit, it does have sufficient cooling output and strong airflow. However, for elongated homes (L-shaped included), you will have to install a fan or two to move the cool air throughout the house.

      A better (yet more expensive) plan would be to get a 12k unit for the bedroom and an 18k unit for the family room and kitchen. Hope this helps.

  16. I have a 1500 square foot single-story house, living, dining, kitchen combined right at 500 square feet, and four bedrooms about 800 square feet. Would the 12k BTU unit for the combined area and a 36k BTU multi room (since it is the only one configured for 4 locations)?

    • Hello Dee, 36k unit will provide sufficient cooling for a 1,500 sq ft home. What will present a bigger problem is how the cold air will be circulated to all 7 rooms; that’s quite a lot. The common solution is by placing some fans that distribute the cool air evenly. The better solution is to get 3 12k units and place 1 in the living room, 1 in the bedroom, and 1 in another bedroom. This option does provide a much better cool air distribution, you won’t run it AC short cycling problems which can happen with 36k unit (more about that here) but it’s also a pricier option. (Sorry for the comment failure error, we’re trying to resolve this issue)

  17. hi I have a sunroom 11ft x 22 ft with 11 foot ceiling. All double pane gas filled widows that slide open. there are 14 windows and bottom kick panels is also glass and the door. I live in south Carolina. The sun shines on the room from early morning to about 4pm. I was thinking of getting a Mr cool mini split 12k unit or would a 18k be better

    • Hello Andrew, that’s a 242 sq ft room with a 38% higher ceiling than an average 8 ft ceiling height room. You would require about 10,000 BTU of cooling output if it were a standard room. However, it’s a sunroom with a whole lot of windows, heavy sun exposure, and located in South California. Those are some substantial factors that increase the cooling BTUs you need. 12k unit would be a bit risky; 18k is a safer bet due to all the sun and hot climate.

  18. Hi
    I have a cinderblock house built in 1950’s. New roof and dual pane windows. Gets pretty warm hear 105-117F dry heat in summer. House is just under 800sq ft/8’ceilings. Not open concept with 4 total rooms and 1/2 bath. I was thinking 24k unit on north wall or 2x12k with 1 unit on north wall and second on east wall. I prefer the later ie 2 of the largest rooms kitchen (north) and living room (east). Your thoughts please. Thank you in advance

    • Hello Tina, first of all, sorry for the comment error, we’re trying to fix it. For 800 sq ft and up to 117F summer heat, you would require about 30 BTU per sq ft. So your calculation – 24,000 BTU cooling output – is spot on. If you had an open concept, the 24k unit might be a good idea. However, with 4 rooms and 1/2 bathroom, the 2x12k units is a more adequate option. You will have a more even distribution of cold air using 2 units. All in all, you have exactly the right idea.

  19. We are getting a 40ft x 8ft steel shipping container with 9’6″ ceilings. It will be framed and spray insulated throughout with a couple of windows. Would 12k BTU be enough?

    • Hello Laura, normally, 12k would be enough. A steel shipping container, however, doesn’t have much in terms of insulation and sunlight on steel can turn it into a sauna. But, even despite that, 12k would be enough in most climates.

  20. Hi I’m looking to install 2 mrcool 3 zone split unit systems in my house.I would like to have each bedroom on separate zone plus separate attic area and 2 units on main floor which is completely open space.rooms are not that big so I’m thinking about smallest units which are 9k btu. My attic is also open space with 400sqft.I think to go with 12000btu here.Finally my main floor is 800sqft . Easiest way is to buy 2x36k btu condensers and split it 3 and 3 and mount them on 2 different walls. First one would be 9k bedroom 12k attic and I was thinking 18k first floor.on the opposite wall I would have 9k bedroom 9k bedroom and 18k first floor.Most of the time at home we spend on first floor so I would like it to be able to cool down fast.that why I was thinking about 2x18k units.Does it sound right or I should go with 2x12k btu for the first floor?

    • Hello Bartosz, your assumptions and calculations are on point. The whole plan sounds pretty adequate. For the 1st floor, 2x12k BTU is enough. If you require a bit faster cooling, a combination of 12k and 18k would be better than 2x18k. With 2x18k you run into problems with oversizing an AC, namely AC short cycling. Hope this helps.

  21. I have been recommended to Mr Cool. Our upstairs is only 500 sq ft, however the small 2 bdrms and the lv/ dn/ kit are all open with 12 ft ceilings. The hallway and bath have very short ceiling. We have all 4 seasons in Missouri. Need guident.

    • Hello, for 500 sq ft and 12 ft ceilings the 12k unit would be too small. If you look at the EPA’s rule of thumb for sizing an air condition, it states that you should calculate 20 BTU per sq ft, if you have 8 ft ceilings. You have 12 ft ceilings; so you’re looking at 30 BTU per sq ft, possibly more. The best Mr Cool unit would be the 18k in this case. Hope this helps.

  22. Hi. I’m confused on the sizing calculation. It says a 12K Mr. cool unit is good for a 500 ft.² room but when you factor in the climate zone (ie zone 5), it’s 50 btu/sq’, or 50×500 = 25000.
    Which is it!? What mr cool unit for my 500 square foot space in Connecticut. Thanks

    • Hello Mike, those specified square footages are usually for cooling; 12k uses 24 BTU per sq ft to get to the 500 sq ft coverage. Of course, if you have higher per sq ft needs (50 BTU), you have to downsize the square footage accordingly. For 500 sq ft with 50 BTU per sq ft, you’ve correctly calculated that you need about 25,000 BTU. In this case, the 24k unit would be adequate, for example.

  23. I have a 650 sq ft shop with a vaulted ceiling of 12′. Well insulated, and adjoined by the house on one side and protected by a garage on the other side. No windows and a 16′ insulated garage door on the south side. Living in Oregon. Will the 18K unit work well?

    • Hello Chris, generally it depends on the level of insulation. With a well-insulated shop, the 18k unit should be pretty adequate, yes.

  24. I am wanting to install a 3 zone mini split in my mobile home thats approx 950sqfeet, I would want one unit in both my bedrooms and one btwn my kitchen and living room and for the life of me I cant figure out what size I need or the line set I would require. My home os 14×65 approx

    • Hello Terry, the simplest way to size an air conditioner is to use the EPA’s ’20 BTU per sq ft (8 ft ceilings)’ rule of thumb. That means for 950 sq ft, you would need about 19,000 BTU unit. 18k unit, for example, should suffice.

  25. I have a 20X20 Garge with 11 foot ceilings, there is also a 16 foot garage door. I was looking at the 12K unit. I live in Cleveland Ohio. Please advise if I am thinking the right way or if there is a different unit. Thanks!!

  26. Hi. I have a 3-car garage, with some extra area. It is 800SF and has an 11″ ceiling. I think it is insulated, but not sure. I’m trying to decide between an electric heater and a ductless mini-split, including Mr Cool since they are a bit less expensive (@Costco) than the Mitsubishi. First of all, do mini-splits do a good job heating garages in a colder climate like Ohio? Secondly, your calculator says I need 21,000 BTU. Should I opt for the 24K model? Any heater-only recommendations would also be appreciated.
    Thanks a lot

    • Hello Mark, for an 800 sq ft 11 ft ceiling garage the standard 1,500W heater won’t cut it. These units generate about 5,100 BTU heating output. You could opt for a 7,500-watt Electric King heaters (check our article about garage heaters; Electric King heaters are at #1). That one produces 25,590 BTU.
      Mini-splits are always a good idea since they reduce the heating costs significantly + you can use them as air conditioners in the summer. The 24k unit would be powerful enough to adequately heat up you garage, yes.

  27. Thanks for all the great info.
    I’m living in the north side of South Carolina and need to cool and heat 800 sq feet room , a 160 sq feet room and a 500 sq foot room.
    I know it going to be a 3 zone unit and it needs to be inverter.
    What size would you recommend.
    This will run off grid system.
    Thanks so much.

    • Hello Tina, first of all, congratulation on the off-grid system. For the smallest room (160 sq ft), you would need the smallest unit (12k, in this case). You might also want to consider an even smaller 5,000 BTU window or 8,000W portable AC. Realistically, you won’t need more than 8,000 BTU for a 160 sq ft room, even in SoCal.

      For a 500 sq ft, the 12k unit should be adequate, but given this is SoCal and it can get quite warm in the summer, the safer option is an 18k unit (you get 36 BTU/sq ft instead of 24 BTU/sq ft the 12k unit would give you).

      For the biggest 800 sq ft room, the 18k won’t cut it in SoCal. The better option would be 24k unit which gives you 30 BTU/sq ft of cooling output. Hope all of this helps.

  28. I am building a detached garage with an upstairs office space (externally accessed). The first floor is a two stall garage with a third stall perpendicular across the back which is a workbench area. The entire first floor is 900 sq ft but I am mostly concerned with conditioning the workbench area periodically when I am in there (the workbench area is also where the first floor head will be located). Most of the time the first floor head would be off or set to keep plumbing from freezing 45 -50 degrees typically.

    The second floor office space is 590 sq ft and I would like it to be able to be conditioned fully when it is occupied (maybe one weekend a month). The two floors would likely never be operated at the same time except to keep from freezing. I live near Seattle. Thanks!

    • Hello Aaron, thank you for a detailed question. The simplest rule of thumb for sizing you can use is the ’20 BTU per sq ft of living space’. So, for 900 sq ft, that would be 18k unit, and for 590 sq ft, that would be 11,800 BTU or 12k unit. With this simple rule, you can calculate a bit what your cooling load needs to be and choose the right size unit.

  29. I am erecting a 1000 sq ft metal building with insulation. It will be open floor space with 11′ eave and 3 to 12 roof pitch on 25′ wide roof. I’m in middle Georgia with hot summers and mid 20’s in winter. would the 24k or 36k work best? And will air handler push air to entire room?

    • Hello Robert, choosing a 24k unit might be a bit risky; 24,000 BTU will hardly be enough for hot Georgia summers and metal buildings. The correct option here is the 36k unit.
      You are right to be concerned with the airflow. It’s quite a challenge for these big 36k units to spread the cool air across a 1,000 sq ft area. However, given this is open floor space, the airflow of the 36k should be sufficient. Alternatively, you can pick two 18k units and install them on the opposite sides; two airflow points are always better than one. Two units will cost you more, of course, you will also have to install both of them but they do provide you with more homogenous cooling and are a bit more energy efficient than the 36k unit. Hope this helps.

  30. I’m interested in the Mr. Cool DIY 36k unit and am struggling with confirming head sizes for my Seattle, WA 1920’s era home (moderate sun/insulation/windows assumptions). Room sizes are: upstairs separated 1bed apt at 612SF, main floor living/dining at 597SF, and two main floor bedrooms at 156SF each. I’m thinking a head configuration of – 18k (upstairs apt), 12k (main living/dining), 9k (bedroom 1) and 9k (bedroom 2) may work okay.. but I’m wondering if the 9k heads may be oversized for the bedrooms and if the 12k may be undersized for the main living/dining area? Is it reasonable to assume that if the 12k unit is slightly undersized that it will be supplemented by the 9k bedroom units, assuming doors are left open during the day? Thanks

    • Hello John, you have the right mind about this. 18k for upstairs will work, 12k for main living as well, 9k are for smaller bedrooms. You are correct, 9k unit might be a bit oversized for 156 sq ft bedrooms but basically, you can’t get smaller than 9k mini split. With a bit undersized main living/dinning room 12k unit, the two 9k units will be more than sufficient is supplementing the cooling output in the main living/dining room if needed. Having that open door is essential, yes, air can’t move through walls. 🙂
      All in all, a splendid setup.

  31. Want to use the 18k mr cool for my 700 sq ft cottage, but want to install two handlers (1 for bedroom and 1 for kitchen/ living room). Is this possible?

  32. This company does not back the products they sell! Cost me over a thousand dollars for shipping labor and coolant to replace a unit that had a leak. The unit started acting up after 8 months. Mr cool could care less about there customers after the sale.

    • Hello Chuck, if you apply 20 BTU per sq ft of living space (8 ft ceiling) rule of thumb, you would need 8,000 BTU for 400 sq ft space. However, you have a 15 ft ceiling (estimated average ceiling height would be about 12 ft), so you have to use 30 BTU per sq ft and 12,000 BTU unit. So, in short, the 12,000 BTU would be exactly on point as far as cooling output is concerned.

  33. I have 700 sqft 3 car garage in Texas which gets extremely hot during the summer months when temperatures are consistently 100+ and really cold during winter. The garage does not have insulation. No insulation in the outside walls or the ceiling or the garage door. Given these circumstances, should I go for 18k or 24k unit?

    • Hello there, those are really big temperature swings. Coupled with no insulation, the bigger unit (24k) is better. Goes nice with everything is bigger in Texas. 🙂

  34. Hi, I have an 1800 sq ft 2-story home in Portland, OR. The house has AC, which keeps the downstairs cool, but the upstairs is always hot in the summers. We’re looking at installing a MrCool to help with the upstairs.

    The upstairs is 900sq ft total and includes a 220sq ft living room and a 135sq ft bdrm on one side of the hall, with 2 100sq ft bdrms (and a bathroom) on the other side of the hall. Would a 2-zone 24k (12k+12k, in the living room and larger bdrm) be sufficient?

    • Hello Matthew, I remember a time when AC in Portland was optional. In recent years, however, it makes sense to prepare for the hot summer. In short, 24k is sufficient cooling output for 900 sq ft. You do have quite a compartmentalized upstairs; hence 2-zone unit is a better choice than a 1-zone unit. The 2-zone 24k unit does seem like an adequate choice, yes. Hope this helps.

  35. We installed an 18k unit about a month ago. Intermittently, I am smelling an “antifreeze “ smell. Any idea what it could be? Thanks.

    • Hello Shirley, the smell of antifreeze is usually associated with a leak in the refrigerant lines; you are probably smelling the refrigerant. Detecting a leak and fixing requires professional help. Maybe you should check with your HVAC guy.

  36. Hello,
    I have a 1076 Sq. Ft. 1 story home. The kitchen, which generates a lot if heat, is on one side if the house with 3 bedrooms on the opposite side of the house. Would it be best to get two 12,000 btu units or one 24,000 btu unit?

    • Hello Michelle, for a kitchen, you usually add 4,000 BTU just because there is a lot of stuff generating heat there. If you apply the 20 BTU per sq ft rule of thumb to your 1076 sq ft home, you are looking at 21,520 BTU. Add those 4,000 BTU and you are at 25,000+ BTU overall cooling output requirements. In short, the 24,000 BTU total output is adequate here.
      Given that your home is quite compartmentalized (3 bedrooms on the opposite sides), it would be better to get two 12,000 BTU units. You will get a much better airflow distribution (and hence more constant temperature throughout the house, without hot spots) with 2 air handlers vs 1 air handler. Hope this helps.

  37. I absolutely love my MrCOOL DIY Mini Split! It’s been a great addition to my home, and I’ve had no problems with it so far. The installation was fairly simple, and the overall design is really cool. I especially appreciate the separate controls for each room, as that makes it easy to adjust the temperature individually. Overall, I’m very happy with my purchase.

    • Hello Deborah, sure, if you fit all the refrigerant and communication lines through there, you can definitely use an existing hole.

  38. How does the heating part work? I live in the Northeast and it can get down to single digits. Will it keep 400sq ft in the 70degree range?

    • Hello Duane, we are currently preparing a chart of COP (coefficient of performance) vs outdoor temperature. Namely, your heat pump should be operating at 3.5 COP or above. At single-digit temperatures, even low temp heat pumps have a below 2.5 COP rating; efficiency falls quite a lot. Supposedly, the same happens with MrCool at low temperatures. Producers don’t quantify how the COP drops at low temperatures but it’s safe to say that at single-digit temperatures, a furnace is much more efficient than any heat pump.

      400 sq ft is not a bit space. 12k unit probably won’t generate enough heat at 0°F to heat it up to 70°. However, 18k unit might just be enough (given that the COP drops by 50%). The best solution for a 400 sq ft is just to buy a cheap 1,500W space heater to supplement the heating when temperatures fall really low. Hope this helps.

      • Thank you. After reading how to size for the correct unit, wouldn’t a 18k be to big for 400 sq ft? If this is a better option, I would buy the larger unit.

        • Hi Duane, 18k is too big for 400 sq ft if you use it as a standard cooling and heating heat pump. However, if you want to get enough heating output at single digit temperatures, however, you kind of have to oversize the unit. The best solution here is to get a 12k unit with a 1,500W heater. At very low temperatures, a heat pump will not be sufficient; so you supplement the heating output with a 1,500W electric heater (it produces additional 5,000+ BTUs).

  39. I installed a 24k DYI unit. Directions were straight forward and it works great.
    Inside fan always runs. Is that normal. After it reaches the set temp the inside unit continues to run in fan mode

    Couldn’t find much in the manual.


    • Hello David, congrats on the DIY installation. For the fan, you have several modes. Check if the fan is on ‘ON’ mode; this would continuously run the fan and its used for air circulation. Switch it to ‘AUTO’ mode; in this mode, the fan works only when it makes sense to run from the AC point of view. Hope this helps.

  40. We have a single story 3000 sq foot home. Do we need need an air handler in each room? We currently have a central air conditioner that is not working and our heat source is gas. Can we keep the gas system for our heat source?

    • Hello Joanne, it is recommended to keep the gas system as a heating source. Even the best low-temperature mini splits like MrCool will have difficulty producing heat at very low outdoor temperatures.

      You don’t need an air handler in each room. 1 air handler can cover 1, 2, or even 3 rooms. The key here is to match the air handler BTU output with the total square footage (12,000 BTU air handler will cool about 500 sq ft) and to ensure airflow between the rooms (open doors). Hope this helps.

  41. I have a garden room 41×10 with all windows on 2 sides. Based on size, the small should work but due to all the windows and the room getting up to 120 degrees when 100 out, wondering if next size up is better. Recommation?

    We installed t he smaller one in another room and it is great.

    • Hello Ken, the combination of a lot of sun-facing windows and below-average insulation (windows have a very low R-value insulation), your conclusion is on point. 12k MrCool would be risky here; 18k is a much safer choice. Hope this helps.

  42. Hi. My daughter’s family has a 9K unit in a kid’s play room (A-09-HP-WMAH-230B) that was in the house when they purchased it. This week they noticed it was not cooling, or at least not cooling like it had been. I noticed that the small 1/4″ line is frosted up and the larger 3/8″ line is warm, which is opposite of a normal split system head pump. QUESTION: where is the expansion device or devices on this unit? Can you point me to a drawing of this Mr Cool unit?

    • Hi Jon, this suboptimal cooling can be caused by something simple like dirty filters (airflow restriction) to something serious like a freon leak. Unfortunately, we don’t have a sketch with the expansion device; in all AC units, the expansion valve should be located between the compressor (outdoor unit) and prior to the indoor evaporator coils. Hope this helps.

  43. Don’t buy from MrCool! They con you with that 7 year warranty. But just try to use it. No one answers the phone. No one calls back. The best you’ll ever get is some uneducated (in HVAC) person asking over and over for weeks via email “what is the problem again”? This is terrible.
    I can not, and would not ever recommend this company to anyone.

    • Hi Randall, thank you for bringing this up. It’s a bit sad that a company producing such great-specs mini splits has subpar customer support. Hopefully, they will do something about that.


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