Sizes of In-Wall Air Conditioners

Definitions

• The size of an in-wall air conditioner often refers to its BTUs or British Thermal Units. A BTU is the amount of energy required to increase the temperature of one pound of water by one degree Fahrenheit, at normal atmospheric pressure. For electrical devices, one kilowatt hour equals 3,412 BTUs per hour. The capacity of cooling systems is often described in BTUs. For example, an air conditioner might be sized at 8,000 BTUs. Wall air conditioners are designed to be installed in a sleeve cut into the wall of a building. Sleeves are often a separate purchase from the unit itself.

Capacity

• Homeowners must choose the correct capacity for their in-wall air conditioner for maximum cooling and energy efficiency. If the capacity is too low, a unit won’t be able to cool a room correctly. If the capacity is too high, a unit may make a room too cold and spend too much energy doing so. Abt Electronics recommends the needed BTUs be based roughly on the square footage of a room. A room from 100 to 150 square feet calls for 5,000 BTUs, while one measuring 300 to 350 square feet needs 8,000 BTUs. At 450 to 650 square feet, air conditioners must be capable of 12,000 BTUs, and at 850 to 1,100 square feet, capacity must go up to 18,000 BTUs.

Considerations

• Square footage is not the only consideration for sizing in-wall air conditioners. "Consumer Reports" lists other important factors. If the mounting wall faces direct sunlight, then the air conditioner requires more BTUs than if it is constantly in the shade. Wall, floor and ceiling insulation affects cooling capacity, and so does the heat from the people occupying a room. A well-insulated bedroom used by a small child requires fewer BTUs than a family room that was converted from a garage and used by six people. The number of windows and whether they face the sun can also affect sizing calculations.

Dimensions

• Another way to size air conditioners is through their physical dimensions, though this should only come after determining the correct BTUs. In general, units with more BTUs are larger, though even units with the same capacity can differ in size. This is important if you have limited wall space. For example, assume you require an air conditioner with a 10,000 BTU capacity. A Frigidaire FRA10EHT2 with that amount measures 20.5 by 24 by 14.5 inches. A Friedrich UE10C33 measures 18.4 by 24.6 by 14.4 inches. And a GE J Series AJCQ10DCD measures 21.8 by 26 by 15.6 inches.