Most people opt for either a ground or air source heat pump because water source heat pumps need a lake, river or stream to work, and the majority of us don’t have these in our garden.
Ground source heat pumps extract warmth from the earth and use it to heat your home or hot water. The (above-ground) pump is connected to a series of pipes (the ground loop) buried in the garden and can be used in all seasons, although you may need a back-up heating system in winter.
Air source heat pumps take heat from the air outside, increase its temperature and use it inside the home. There are two types - air-to-air pumps and air-to-water pumps. The former produce warm (and also cool) air and circulate it through fans. Air-to-water pumps supply your home’s (wet) central heating system. Air source heat pumps can work at temperatures as low as -15 degrees celsius outside, but can be less effective when it’s colder than -5 degrees celsius, so, again, another form of heating may be necessary in winter.
If your home’s heated by radiators, they won’t get as hot with a heat pump as they would with a boiler - you’ll need to have them on for longer or replace them with more powerful ones. The perfect partner for a heat pump is wet underfloor heating because both work at lower temperatures. However, wet underfloor heating isn’t particularly easy or cost-effective to retrofit - it’s often better to install it when renovating or building a house.
Heat pumps warm the air gently, so they’re not ideal if your home heats up and cools down quickly. They work most efficiently in homes with good insulation and draught proofing - see my How-to Tip.