Having an oversized air conditioner or heat pump sounds like a great idea. Right? Wrong - In reality oversized cooling equipment costs more to purchase, increases your electric costs, and decreases your comfort. Here's why:

• The unit turns on and off more frequently because it is designed to cool a larger space. This places stress on the unit and will increase ongoing maintenance expenses while shortening the life of the unit.
• The unit does not run long enough to reach rated efficiency levels. Equipment reaches design SEER/EER ratings only when operating at design intervals between start-up and shut-down as controlled by the thermostat.
• The unit does not properly reduce moisture content of the air so you are less comfortable than if the unit were properly sized.

It takes a trained expert to determine proper sizing of a cooling unit. Many factors go into a complete Heating and Cooling Load Analysis to select the correctly sized equipment. As a rough rule-of-thumb you need one ton of air conditioning per 400 to 500 square feet of living space in the Phoenix area. Rule-of-thumb is something we use in the field as inspectors, heating and cooling contractors to determine equipment sizing should not use it. If the replacement contractor does not provide a Heating & Cooling Load Analysis then consider finding another contractor.

APS estimates typical annual wasted energy costs from oversized equipment to be between $60 and $300 per 3-ton unit. Add in the cost of early system replacement and higher than average maintenance expenses to determine the real financial impact. When your inspector notes oversized or undersized equipment it is an important finding.