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Basics of how heat pumps works, their features and efficiency.

Choosing equipment, designing duct systems, proper installation.

Bid comparison worksheet

How Does A Heat Pump Work? It moves heat from outside to inside to heat your home in winter. In the summer, it cools by moving heat from inside to outside the home.

Types of Heat Pumps

Main Parts of a Heat Pump

The outdoor unit includes the outdoor heat exchanger, compressor and a fan.

The indoor unit includes the indoor heat exchanger and a fan. Some indoor units also have a compressor. Refrigeration lines connect the two units.

Heat Pump Efficiency or COP, Coefficient of Performance. COP is the ratio of heat output to electrical energy input.

The outdoor unit goes into a defrost cycle when temperatures drop below 40° F. To melt ice that builds up on the coils, heat is drawn from the house to warm the outdoor coils.

Back-up, Emergency or Auxiliary Heat is available to add supplemental heat when outdoor temperatures are too cold for the heat pump to adequately heat the house. Electric resistance coils come on in the Auxiliary mode to bring the house up to a comfortable temperature when the heat pump can not adequately do the job.

The Balance Point

When you plot the heating requirement of the house and the output of a heat pump you get a graph that looks like the figure below. As the outdoor temperature drops, the output of the heat pump decreases. At the same time the heating requirement of the house increases. At some temperature (31° F in our example), the heat pump output and the home heating requirements match. This temperature is called the balance point. Below the balance point temperature, supplemental heat will be required.

The heat pump's heating capacity ("size") should be selected based on a desired balance point. In climates where heating is the main concern, sizing may be a compromise between heating and cooling requirements. The chosen balance point varies according to climate. Typical balance point temperatures are in the 27° F to   35° F range. (Source: Heat Pump Buyer's Guide, Bonneville Power Administration, July 1995).

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This page was last updated on 26-Jun-2005

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