When selecting an air-source heat pump, consider the following three characteristics carefully: the energy efficiency rating, sizing, and the system's components.

 
Sizing

It's important that you choose the right size heat pump needed for your home. Bigger is not better. Oversizing causes the heat pump to start and stop more frequently, which is less efficient and harder on the components than letting it run for longer cycles. A properly sized heat pump also will provide you with better comfort and humidity control than an oversized one.

The heating and cooling capacity of heat pumps is measured in Btu per hour. The cooling capacity is commonly expressed in "tons" of cooling capacity —- each ton equaling 12,000 Btu per hour. Correct sizing procedures involve complex calculations, which are best performed by an experienced contractor, who uses sizing methods accepted by the heat pump industry.

Don't employ a contractor who guesses the size of the heat pump needed. Rule-of-thumb sizing techniques are generally inaccurate, often resulting in higher than necessary purchase and annual energy costs.

 
System Components

You and your contractor should discuss options that will help improve your home's comfort and the economy of your heat pump. Regarding ducts, for example, it's important to carefully consider their design and materials, as well as the proper amount of space they require.

Check your home's blueprints to see if the architect and builder have planned adequate space for ducts and fans. Heating and cooling contractors complain that they often have to squeeze heating and cooling systems into spaces that are too small, resulting in constricted ducts and inadequate airflow.

Except for packaged systems, you'll also need to select the proper type of indoor coil for adequate summer moisture removal.

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