I was watching Homes under the Hammer, and a lovely Thatched cottage was being renovated. The oil heater was replaced by an air source heat pump, with an immersion heater that looked like a nuclear power generator.
What is an air source heat pump?
An air source heat pump (ASHP) is a system which transfers heat from outside to inside a building, or vice versa. Under the principles of vapor compression refrigeration, an ASHP uses a refrigerant system involving a compressor and a condenser to absorb heat at one place and release it at another.