Heat pumps are replacing gas boilers in the UK and Europe and are increasingly common across the United States. In India, every air conditioner is already a heat pump running in one direction. Understanding how they work explains why they are central to cutting energy bills and emissions.
A heat pump moves heat, it does not make it
A boiler or electric heater turns fuel or electricity directly into heat. A heat pump instead moves heat that already exists from one place to another, using a refrigerant that evaporates and condenses in a loop. Even cold outdoor air contains useful heat energy, and the pump concentrates it and delivers it indoors.
Because it moves heat rather than creating it, a heat pump can deliver three or four units of heat for every unit of electricity it uses. Engineers call this ratio the coefficient of performance, or COP.
The four-step refrigeration cycle
- Evaporate. Cold liquid refrigerant in the outdoor coil absorbs heat from the air and boils into a gas.
- Compress. The compressor squeezes the gas, which sharply raises its temperature.
- Condense. The hot gas releases its heat indoors, into radiators, underfloor pipes or air, and turns back into liquid.
- Expand. An expansion valve drops the pressure, cooling the liquid so the cycle can start again.
Reverse the flow with a valve and the same machine cools your home. That is exactly what your split AC does in summer.
Running cost: heat pump vs gas vs electric heater
Whether a heat pump saves money depends on the price of electricity compared with gas where you live. In countries where electricity costs three or four times as much per unit as gas, a well-installed heat pump roughly breaks even on running costs while cutting emissions. Where electricity is cheaper relative to gas, savings are larger.
Air source or ground source?
- Air source heat pumps take heat from outdoor air. They are cheaper and simpler to install, and the most common choice.
- Ground source heat pumps take heat from pipes buried in the ground, where the temperature is steady all year. They are more efficient in very cold climates but much more expensive to install.
What makes an installation succeed
- Insulation first. A leaky house needs a bigger, costlier unit.
- Correct sizing. Installers should calculate the heat loss room by room, not guess.
- Low flow temperatures. Heat pumps are most efficient delivering gentle warmth around 35 to 45°C, so larger radiators or underfloor heating help.
- Grants. The UK, US and many European countries offer grants or tax incentives. Rules change often, so check your government's current scheme before buying.
Frequently asked questions
Do heat pumps work in freezing weather?
Yes. Modern air source heat pumps keep working well below freezing, although efficiency drops as it gets colder. They are widely used in Scandinavia.
Is my AC a heat pump?
An AC is a heat pump that only moves heat out of the room. Models sold as "hot and cold" or "heat pump" ACs can reverse to heat the room in winter.