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How does a heat pump work?

It seems like magic, getting heat out of a colder place and moving it to a warmer one. You have at least one heat pump in your house already - your refrigerator - and if you have air conditioning you have another. How does this magic work? Rather than burning fuel to make heat, a heat pump uses electrical energy to move heat. This is much more efficient.

Heat pump heating happens in a four stage continuous cycle:

  1. A liquid refrigerant absorbs energy from the outside air in coils of pipes in an evaporator, turning the refrigerant from liquid to a gas. The evaporator will exhaust cooler air.

  2. The refrigerant is then pressurized by the compressor pump, which raises its temperature higher than the indoor temperature.

  3. The hot gas flows through coils of pipes in the condenser giving off this heat to the room and turning back into a liquid, like the moisture condensing on cold window glass from the warm moist air from your shower.

  4. The liquid finally flows back through an expansion valve that reduces its pressure, hence cooling it down so it can repeat the cycle.

Heat Pump illustration(3).jpg
How a heat pump works

This is the same cycle used in a refrigerator or air conditioner. In a fridge or freezer, the evaporation happens in pipes inside the refrigerator cabinet, pulling the heat energy out of the fridge air to to cool it. The condenser coils under or behind the fridge expel the heat into the room. In an air conditioner, the cycle is reversed so that the evaporation happens in indoor pipes, pulling heat energy from the indoor air. The condensing happens outside, expelling the heat to the outdoor air.

A heat pump can both heat and cool, using a reversing valve to change the direction of the refrigerant and reverse the heat pump function.

This cycle is described above as it works for an "air-to-air" heat pump heating (or cooling) the air in a house transferring heat energy to or from from the outside air. A heat pump uses the same principles, however, for transferring heat energy to or from water - as in a heat pump water heater or radiant floor heater - or in a ground source heat pump transferring heat energy to or from the earth.

What should I look for when buying an induction cooktop?

Check out the Buying Tips for an Induction Range/Stove or Cooktop for a biased personal guide to induction cooktop features​

Buying Induction
Magetic Fields & Induction Cooking

Are magnetic fields from induction cookstoves bad for you?

A review of scientific studies of induction cooking concluded that induction cookstoves are likely far better for our personal health than burning gas to cook in the home. It did provide some precautionary suggestions for safest use.

● Induction cookstoves are not likely to cause disruptive interference for most modern pacemakers or related implants at normal cooking distances. Implant users should, however, consult with their medical professional and manufacturer for specific guidelines for their device and on safe distances to keep between them and the front of the burner in use. Where guidelines are provided they usually recommend a burner to device distance of one foot and occasionally two feet. 

● Induction cooking is not likely to cause any significant problems for the rest of us, including fetuses and young children. However a reasonable precautionary measure, would be to use the back burners for extended high power uses (like boiling a large pot of pasta water), particularly for pregnant women and when young children are helping at the stove. 

For more studies on health issues of cooking with gas or electric see our section on Building Electrification Studies -
Health issues with indoor cooking comparing gas and electric

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