How do I know my air conditioner is sized properly?

The square footage, eyeball, and "beer can cold" methods are not acceptable means by which to size a Heating, Ventilation, & Air Conditioning (HVAC) system. However, many contractors still use these archaic techniques. When replacing an existing unit, selecting the same size unit may not acceptable either, unless the unit size is proven with calculations. An oversized unit will cost more and use more energy than necessary. An undersized unit will be over stressed and will probably fail sooner, not to mention unable to provide the required heating and cooling.

Technical improvements in mechanical units, such as variable speed air handling and higher efficiencies, have made many past sizing strategies obsolete. Fortunately, there are now established national standards by which to size HVAC systems for a home. Many factors can impact these calculations including insulation, doors and windows, floor area, ceiling heights, orientation, etc.

Make sure your mechanical contractor prepares the proper load calculations and includes these as a part of their work. Alterntively, you can hire an independant consultant to perform the HVAC system design and load calculations. Once installed, verify the installtion with certified testing. If in doubt, consult with your architect to assure you are getting a properly sized air conditioner and heater.