Heat pumps do not make heat; they move it from one place to another. The one shown here is the most common type, an air-source heat pump which takes its heat from the air outside. There are also ground-source, and water-source heat pumps.
Heat pumps are most efficient (and so cost least to use) when they run at lower temperatures. New heating systems should be designed to work at no more than 55ºC, and ideally a lot lower.
Over the whole year, for every kWh of electricity used a heat pump can typically produce 3 or more kWh of heat.
A lot of our electricity in the UK is already supplied from renewables so heat pumps are a way to reduce CO2 emissions, especially if you use a truly renewable electricity supplier.
Replacing an oil or gas boiler? You may qualify for a £5000 Boiler Upgrade Scheme grant.