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• How to choose an air conditioner
• How much cooling capacity do I need?

How to choose an air conditioner for window or through-wall mounting, how much BTU capacity do you need? Also see RATED COOLING CAPACITY How to determine the cooling capacity of air conditioning equipment. © Copyright 2008 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use the links at page left to navigate this document or to go to Other Website Topics. Green links at left show where you are in our document & website.

Typical BTU Cooling Capacity Range for Air Conditioners

Portable, window, or through-wall air conditioners are typically described by their manufacturer as suited for:

• Single Room Air Conditioner Capacity - typically for rooms up to 20' x 20' or 400 sq.ft. in area. BTUs in this product range are typically from 6,000 BTUh to 10,000 BTUh.
• Multiple Room Air Conditioner Capacity - typically for a total area of up to 800 sq.ft. BTUs in this product range are typically from 10,000 BTUh to 16,000 BTUh.
• Large Capacity Air Conditioner Capacity - typically for multiple rooms or very large rooms up to a total area from 900 sq. ft. to 2,000 sq.ft. BTUs in this product range are typically from 16,000 to 28,000 BTUh.
• Central Air Conditioning - typically to cool an entire floor or multiple floors in a home. Also see A/C TYPES, ENERGY SOURCES

To determine the BTUs needed to cool a given space follow this procedure:

1. Calculate the total square feet to be cooled: Measure the size of the room (or rooms) to be cooled, to obtain total square feet. Multiply room length by width for each room and if there are multiple rooms, add the room areas together to get a single number.
2. Read the Base BTUs needed from Table 1 below
3. Add additional BTUs for these factors:
• + 4,000 BTUs for each room below a ceiling or roof which is not insulated
• + 4,000 BTUs for a home or residential kitchen included in the cooled area
• + 1,500 BTUs for each window which receives significant daily sunshine
• + 1,500 BTUs for a room over a kitchen or boiler room IF the kitchen or boiler room is actively producing heat during the cooling period
• + 600 BTUs per person over two, if more than two occupants will be occupying the room during the cooling period
4. Subtract BTUs from the total required if these factors are present:
• - 1,000 BTUs if the room is on the shaded side of the building
5. Calculate the final total BTUh needed from the above steps. This should place you in the right range of cooling capacity needed. Review the warning below about buying an oversized air conditioner.

The table below gives recommended air conditioning BTU's necessary to cool a single room. The data in the table assumes that the ceiling over the room is insulated and that the room is not over or is not itself a special heat-producing area such as a kitchen or boiler room.

Do not buy an air conditioner which is oversized (too many BTUh) for the area you need to cool. You may think that bigger is better, but not in the case of air conditioning. To make a room comfortable the air conditioner needs to both cool the room air AND dehumidify the room air. If the air conditioner is too large for the space to be cooled, the temperature will drop quickly and the A/C unit will shut off before the air has become adequately dry. The room will be either too cold or too humid for comfort.

Other types of portable or individual-area air conditioners

• Heating & Cooling units - capable of both cooling or heating a room using electricity. Basically these units are small heat pumps that are mounted in a building window or wall. Heating/Cooling units will give two different BTUh figures, one for cooling and one for heating. These figures will differ, for example, producing 18,000 BTUh in cooling mode but only 12,000 BTUh in heating mode. The difference between heating and cooling, and the amount of heat actually available will depend also on the outdoor temperatures when in heating mode (as with any heat pump system, the unit cannot provide heat below certain temperatures.)
• Slider or Casement Window units - narrow tall cooling systems which are designed to fit into the narrow space provided by casement or slider windows.
• Through-wall air conditioners - air conditioning units which are designed to be installed into a metal sleeve which is then itself installed in an opening cut into the building wall, leaving windows unobstructed, or perhaps for use in a room without a suitable window in which an air conditioner could be placed. BTU output is typically a bit more than the smallest window air conditioners but otherwise is similar in range.
• Portable air conditioners - units on wheels which are plugged into an outlet but can be moved room-to-room and do not require a window for their exhaust. These cooling units are of modest cooling ability, typically around 10,000 BTUh.

AIR CONDITIONING SYSTEMS Chapter Index

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Technical Reviewers

Particular thanks are due to experts and also consumers who read these articles and suggest corrections, changes, and additions to the material. Content suggestions, technical corrections and content critique are invited for any of the content at our website.

• Daniel Friedman - editor
• Thanks to various industry and air conditioner sales publications and consumer pamphlets including Sears Kenmore(R) air conditioning sales
• Critique, contributions wanted: Contact Us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution.

More Reading

• RATED COOLING CAPACITY How to determine the cooling capacity of air conditioning equipment

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