There are a number of metrics you should know before buying an air conditioner. You have different EER and SEER ratings, power, amperage, voltage, and so on.
The most important metric is the BTU value. 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 a 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):
In short, you would need a 10,000 BTU air conditioner.
How many BTUs do you need to properly cool down certain square footage of space?
There are only 2 rules:
- Not too big. Obviously, you don’t want a 14,000 BTU window air conditioner for a small 12×12 room because it unnecessarily boosts your energy bill.
- Not too small. You don’t want to get hot in the summer because you bought a 6,000 BTU portable air conditioner for a 1,000 sq ft apartment.
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
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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.
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 very small 12×12 room, for example. According to the US Department of Energy directive, the most appropriate size of an air conditioner would be 2,880 BTU unit. The best you can do here is to buy a small 5,000 BTU window or small 8,000 BTU portable AC unit (more about 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 just 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 or an air conditioner you need, let’s have a look at a BTU chart:
Air Conditioner BTU Chart
|Room/Area Size:||Examples:||Recommended BTU:|
|100-200 sq ft||10x10 room, 12x12 room, 14x14 room||4,000 BTU air conditioner|
|200-300 sq ft||16x16 room, tiny apartment||6,000 BTU air conditioner|
|300-400 sq ft||18x18 room, 20x20 room||8,000 BTU air conditioner|
|400-500 sq ft||22x22 room, small studio apartment||10,000 BTU air conditioner|
|500-600 sq ft||24x24 room, average studio apartment||12,000 BTU air conditioner|
|600-700 sq ft||2 rooms, small apartment||14,000 BTU air conditioner|
|700-800 sq ft||2 rooms, average apartment||16,000 BTU air conditioner|
|800-900 sq ft||3 rooms, above average apartment||18,000 BTU air conditioner|
|900-1,000 sq ft||3 rooms, larger apartment||20,000 BTU air conditioner|
|1,000-1,200 sq ft||4 rooms, large apartment||24,000 BTU air conditioner|
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 in 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 chill cold room and more than $100/year unnecessary cost on your electricity bill.
Perfect BTU Air Conditioner For Room Sizes
The ballpark figure, as recommended by The U.S. Department of Energy, is 20 BTU per sq ft. That is a very good estimate already.
The simplest BTU calculation formula for 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 take into account some additional factors. These are:
- Room height.
- Local climate.
- Sun exposure.
- 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 building have +10 ft ceilings), you have to add a bit of cooling power in terms of BTU.
There is also a difference if you live in Texas or in New York. The local climate in Texas in, 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:
- If you have high walls.
- If you live in a hot climate. Examples: California, Texas, Florida, New Mexico, and so on.
- If the particular room you want to cool down is facing the sun more often than not.
- 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’re should be looking at 10,000 BTU air conditioners (as recommended). You should be looking at a 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 BTU should our air conditioner have.
The equation for ‘sq ft to BTU’ is quite simple – just multiply the sq ft with 20. That means that a 500 sq ft room needs a 10,000 BTU air conditioner. Do make sure, of course, 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.
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 one you should take), you can ask in the comments and we’ll try to give you an answer as soon as possible.