[Acuario]

Good explanations so far but where does the heat come from that is used to heat the house?

Well, if you have ever pumped up a bicycle tyre you will probably have noticed that the pump body gets warm or hot. How come?

When you compress a gas it heats up - pumping the pump with mechanical energy (your arm or leg) compresses the gas to a higher pressure (as the exit from the pump is a small hole so the pressure in the pump body increases) and the gas heats up.

This is what the compressor does - compresses the refrigerant which is in the form of a cold gas with mechanical energy (a motor) into a liquid and in doing so as the gas compresses and as it turns to liquid it heats up. The liquid refrigerant then boils into a gas absorbing even more energy and becoming even hotter (super heat).

The super heated gas is then pumped to the place where the heat is removed (some form of heat exchanger), the gas cools and condenses into a liquid releasing its heat so you then have a cold liquid. This cold liquid is vaporised into an even colder gas through a metering device. The very cold gas then easily absorbs heat from the atmosphere or ground (in another heat exchanger) to become a cold gas and this then goes back into the compressor to be compressed back into a hot liquid then super heated gas.