How Does a Heat Pump Get Heat from Cold Air?

We have had a few calls lately with folks asking how a heat pump can really keep their house warm in the cold winter weather. They want to know the science behind the mechanism and understand how it is really possible to extract heat from cold air. The process is pretty simple and very similar to how an air conditioner or a refrigerator works.

Maybe it is hard to grasp because when we go outside into colder winter temperatures, our bodies get cold. Since our personal experience of cold air is a cooling effect, we may wonder how that same air could actually heat anything up.

But, there is always heat present in air unless the temperature is absolute zero.

Heat flows when there is a temperature difference. So in order to get heat out of 30 degree air, you have to put in contact with something that is below 30 degrees. That something, in the case of a heat pump system, is refrigerant.

The compressor circulates refrigerant that absorbs and releases heat as it travels between the outdoor and indoor units.

In the compressor, the liquid refrigerant is pushed through an expansion valve and magic happens. The liquid refrigerant becomes a gas and the temperature drops A LOT. The cold outdoor air then becomes the warmer object in relation to the refrigerant. Heat, by nature, moves from warmer to cooler objects. So now it moves from the outdoor air through the system and into your home.

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