To buy an energy-efficient room air conditioner, you must first determine what capacity, or size, you need. This is important for two reasons:
Use the simple calculation method described below to estimate the cooling capacity you'll need to maintain a temperature of 24°C with a humidity level of between 30 and 50 percent. You can find a more detailed calculation method in another NRCan publication entitled Air Conditioning Your Home (the "Useful Information Sources" page explains how you can order this booklet or view it on-line). If you're cooling a large space, consult a qualified contractor who will consider such factors as the amount of space to be cooled, the number of occupants, the insulation levels and the size, orientation and R-value of windows and doors.
To calculate floor area, multiply the length of each room or open space by its width. Don't estimate – take a few minutes to measure accurately. Units are often bought to cool one or two rooms. Enter your numbers into the blanks provided. (The calculation for a typical open-concept living/dining room will guide you through the process.)
|LENGTH||x||WIDTH||=||FLOOR AREA OF SPACE TO BE COOLED|
|6.1 m||x||3.7 m||=||22.6 m2|
|(20 ft.||x||12 ft.||=||240 sq. ft.)|
Remember to combine the total floor area of all the space you'd like to cool with a single air conditioner.
Use this table to find the basic cooling capacity in Btu/h you'll need based on total floor area to be cooled.
|TOTAL FLOOR AREA||BASIC COOLING CAPACITY|
|111–149||1200–1600||19 000–24 000|
|149–167||1600–1800||24 000–27 000|
|167–260||1800–2800||27 000–33 000|
*Based on rooms with two occupants and average windows, insulation and sun exposure.
|TOTAL FLOOR AREA TO BE COOLED||BASIC COOLING CAPACITY|
|22.6 m2 (240 sq. ft.)||NEEDS||6000 Btu/h|
Note: If cooling capacity is more than 12 000 Btu/h, consider installing two smaller units. Otherwise, a single unit might require a larger amperage circuit (20–30 amperes) or a dedicated 240-volt circuit; consult an electrician for more information.
|Additional Sizing Considerations||
Add to or Subtract
|If the space faces due north or northeast or is heavily shaded, subtract 10 percent of the basic cooling capacity.||+ 600||
|If the space is extremely sunny (e.g. windows face west and southwest), add 10 percent of the basic cooling capacity.||
|If the space is poorly insulated, add 15 percent of the basic cooling capacity.||
|If the space includes a working kitchen, increase cooling capacity by 4000 Btu/h.||+ 4000||
|If more than two people regularly occupy the space, add 600 Btu/h for each additional person.||___ (number of additional people) x 600 =
|If the air conditioner will run only at night, subtract 30 percent of the basic cooling capacity.||
Approximate size of room air conditioner to buy
|10 600 Btu/h|
Source: Natural Resources Canada (NRCan) - Office of Energy Efficiency