Air Source Heat Pumps (ASHP) absorb heat from the outside air, using the same technology that is found in refrigerators. This heat can then be used to heat radiators, underfloor heating systems, or warm air convectors and hot water in your home. ASHP extracts heat from the outside air, even in temperatures as low as –15°C.
There are two main types of ASHP systems: Air-to-Water and Air-to-Air.
Heat pumps work in the same way as refrigerators, but instead of removing heat from a box in our kitchens and expelling it outside, heat pumps use heat from outside to warm our homes. The process has four stages: heat extraction, compression, heat rejection, expansion.
Heat extraction. Heat from the outside air is absorbed at low temperatures into a refrigerant fluid inside a pipe.
Compression. The refrigerant then passes through a compressor that raises it to a higher temperature.
Heat rejection. This heat contained in the refrigerant is exchanged with either air or water inside the home, depending on the ASHP system in place. An Air-to-Water system distributes heat either through a wet central heating system (i.e., large wall hung water-filled radiators) or underfloor piping. An Air-to-Air system instead produces warm air which is circulated by fans (i.e., warm air system) to heat the home.
Expansion. The cooled refrigerant returns outside where it absorbs further energy from the outdoor air in a continuous process, for as long as heating is required.
ASHP work at lower temperatures over longer periods of time compared with gas boilers. These systems work best in well-insulated and draught-proofed homes, particularly in homes with a high thermal mass.
Installing an ASHP can cost £9,000 to £11,000 but could be higher. The running costs are low, however they depend on the size of the home and the existing insulation. The life expectancy of ASHP is about 20 years.
|Existing System to be replaced:||Fuel Bill Savings by replacing the old system (£ per year):||Carbon Dioxide Savings by replacing the old system (kg/year):|
|Gas older (G-rated)||£395 – £425||4,450 – 4,750 kg/year|
|Gas newer (A-rated)||-£95 – -£100||2,150 – 2,250 kg/year|
|Oil older (G-rated)||£500 – £550||7,100 – 7,600 kg/year|
|Oil newer (A-rated)||-£80||3,650 – 3,900 kg/year|
|LPG older (G-rated)||£1,200 – £1,300||5,400 – 5,800 kg/year|
|LPG newer (A-rated)||£380 – £410||2,700 – 2,850 kg/year|
|Electric Storage Heaters (G-rated)||£920 – £1,000||3,450 – 3,750 kg/year|
|Electric Storage Heaters (A-rated)||£520 – £560||2,400 – 2,600 kg/year|
|Coal||£315 – £350||9,800 – 10,500 kg/year|
A number of financial incentives can help with the cost of this technology. These include the Green Homes Grant Local Authority Delivery scheme and Renewable Heat Incentive. Learn more about these options.