Air source heat pumps (ASHP) look like air-conditioning units, but are used to heat rather than cool homes. In the same way that a refrigerator removes heat from its inside and transfers to its outside, so an ASHP takes heat energy from the outside air and transfers this to a central heating system on the inside of the property. Such a central heating system might be warm air convector heaters, underfloor systems. Electricity is needed to drive the heat pump but, depending upon the outside air conditions, the ASHP may be able to transfer three times as much heat energy as would be produced if this electricity was simply used as the source of the heat. ASHPs qualify for the Government’s Renewable Heat Incentive (RHI). With underfloor heating, it can take several hours for a room to be heated-up, so the user must plan-ahead. Generally, the efficiency of an ASHP declines with lower outside air temperatures and higher air humilities.
Pros: Qualifies for RHI payments, can be used with underfloor heating or central heating, little outdoor space needed for the unit, efficient in converting the electricity that powers the unit to heat. Can be used with wet radiator systems – but less efficient if used in this way.
Cons: Underfloor systems are expensive to retro-fit and best suit new builds. Low flexibility, as underfloor heating takes much longer to warm up a room compared with wet radiators or electrical heaters. Less efficient in a cold snap, some noise generated by outdoor unit.
Indicative annual cost: with wet radiators – £1,049; with underfloor heating £815