How to Measure How Many BTUs You Need for AC in a Room

Determining the required British Thermal Units (BTU) per hour to properly air condition a room is relatively simple. The BTU requirement is based on the room's size. Buying the proper size unit will ensure the system you invest in will perform well in the room in which it is installed.

Tape measure

Instructions

- 1
  Measure the square footage of the room to be cooled. Measure the length and width of the room. You may need a helper to hold the other end of the tape measure.
- 2
  Calculate the BTUs required by multiplying the square footage of the room by 20. For example, if the room is 10 feet by 12 feet, multiply 10 X 12 X 20, for a result of 2,400.
- 3
  Consider other attributes of the room. For example, if the room is shaded, subtract 10 percent of the calculated BTUs. For the above example, subtract 240 for a result of 2,160. If the room gets a lot of sun, add 10 percent. You also may wish to buy a unit that provides more BTUs per hour for a room with poor insulation. If the room is a kitchen, add 4,000 BTUs. Add 600 BTUs per person if more than two people will use the room on a regular basis. Rooms with high ceilings and those with many large windows will require more BTUs.

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