What Is a BTU?


  • A BTU or British Thermal Unit is a measurement of how much energy is required to raise the temperature of one pound of water by one degree. That might not sound useful when it comes to air conditioning your home or business but the underlying calculation is critical to staying comfortable.


  • Each air conditioner or heater is rated to produce a certain number of BTUs. Many factors go into calculating BTUs, so we have put together a set of tools to help with air conditioner sizing.


What Size Air Conditioner Do I Need?


  • Size matters. Especially when choosing the correct BTU size for an air conditioner. Choose too small a unit, you could end up with a room that’s not cool enough, or with an air conditioning unit that overheats. On the other hand, too large a unit for the space will not remove the necessary moisture from the room, making it feel clammy and uncomfortable. Here’s how to calculate BTU to find the perfect AC unit for your needs.


Air Conditioner BTU Chart.


  • The chart below is a great starting point for sizing your AC. These BTU calculations are based on a standard room with 8-foot ceilings, two windows and one door. If the room has more windows, doors or higher ceilings, adjust the BTUs upward.


  • Other factors in determining the BTU size would be the room’s purpose. Kitchens normally have more heat thanks to stoves and ovens, and rooms with computers and other electronics give off extra heat. Therefore, these rooms would require bumping the air conditioner size up.


Square Feet BTU’s
0 – 150 5,000 BTU
150 – 200 6,000 BTU
200 – 250 7,000 BTU
250 – 300 8,000 BTU
300 – 350 10,000 BTU
350 – 400 12,000 BTU
400 – 450 14,000 BTU
450 – 500 15,000 BTU
500 – 600 18,000 BTU
600 – 700 20,000 BTU
700 – 800 22,000 BTU
800 – 900 25,000 BTU


  • The above BTU figures are estimates based on an average room (2 Windows, 1 Door, 8 foot ceilings). Other variables will have to be taken into consideration when figuring BTU sizes e.g. Kitchens, High Ceilings, Sky Lights, Large Windows, Use of Room, and Occupants, etc. For more details or help please send us an email at sales@wasi.lk.

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