Every residential heat pump sold in this country has an EnergyGuide label, which displays the heat pump's heating and cooling efficiency performance rating, comparing it to other available makes and models.

Heating efficiency for air-source electric heat pumps is indicated by the heating season performance factor (HSPF), which is a measure over an average heating season of the total heat provided to the conditioned space, expressed in Btu, divided by the total electrical energy consumed by the heat pump system, expressed in watt-hours.

Cooling efficiency is indicated by the seasonal energy efficiency ratio (SEER), which is a measure over an average cooling season of the total heat removed from the conditioned space, expressed in Btu, divided by the total electrical energy consumed by the heat pump, expressed in watt-hours.

In general, the higher the HSPF and SEER, the higher the cost of the unit. However, the energy savings can return the higher initial investment several times during the heat pump's life. A new central heat pump replacing a vintage unit will use much less energy, substantially reducing air-conditioning and heating costs. 

To choose an air-source electric heat pump, look for the ENERGY STAR® label. In warmer climates, SEER is more important than HSPF. In colder climates, focus on getting the highest HSPF feasible.

These are some other factors to consider when choosing and installing air-source heat pumps:

Select a heat pump with a demand-defrost control. This will minimize the defrost cycles, thereby reducing supplementary and heat pump energy use.

Fans and compressors make noise. Locate the outdoor unit away from windows and adjacent buildings, and select a heat pump with a lower outdoor sound rating (decibels). You can also reduce this noise by mounting the unit on a noise-absorbing base.

The location of the outdoor unit may affect its efficiency. Outdoor units should be protected from high winds, which can cause defrosting problems. You can strategically place a bush or a fence upwind of the coils to block the unit from high winds.