Heat pumps: How do they work, what do they cost and are they noisy?

Andrew Aitchison/Getty ImagesThe government's Warm Homes Plan promises £15bn to help UK households pay for green technologies such as heat pumps, as part of its efforts to drive down energy bills and cut planet warming emissions.Heating homes accounts for about a fifth of the UK's planet-warming emissions, so switching from gas and oil to heat pumps is seen as a priority.What are heat pumps and how do they…