Heat Pumps: How to they work and how much do they cost?

The government is to offer £5,000 to people in England and Wales to replace their gas boilers with heat pumps.

It is part of efforts to reduce greenhouse gas emissions in the UK.

What do heat pumps cost and what is the deal?

Heat pumps are quite costly - between £6,000 and £18,000, depending on the type and the size of your home.

The £5,000 subsidy - available from next April - will bring the price closer to that of installing a new gas boiler.

Currently, gas heating accounts for 21% of the UK's carbon emissions.

No new gas boilers will be sold after 2035.

How does a heat pump work?

A heat pump is an electrically powered device that absorbs heat from the air, ground or water around a building.

For example, air-source pumps suck in outdoor air and pass it over tubes containing refrigerant fluids to produce heat.

Will it be cheaper to run than a gas boiler?

Right now, given the soaring price of gas, it's possible, but it's not clear whether heat pumps will be cheaper to run in the long run.

The government says it will look at measures to ensure heat pumps are no more expensive to run than a gas boiler.

Can I install a heat pump at my home?

It's easiest to put them in new builds, but older homes can also be fitted with heat pumps.

Most domestic heat pumps will extract heat from the air.

A box of about one metre by one metre needs to be outside (close to or attached to the property) to draw in air.

It should be at least one metre from your neighbour's property so they will not be able to hear it, although it shouldn't be much louder than your fridge.

You also need space inside for a heat pump unit and hot water cylinder. The unit will be about the size of a gas boiler - while the cylinder depends on the size of the home.

A ground source heat pump needs much more space outside: either a bore hole as much as 100m deep; or a horizontal system dug into the ground over a large area.

What are the drawbacks?

Installation can be difficult and expensive - you may need bigger radiators or to dig into floors.

And the high levels of insulation needed aren't always possible in older, solid-walled homes common across the UK.

Engineers who are trained in installing and servicing heat pumps are - for the moment, anyway - harder to find.

And it is unclear whether people renting their homes will have a way to insist on them being warmed by heat pumps.