The Renewable Heat Experts Guide to: Getting to know Heat Pumps.

Stokes - Heat Pump + House


(Source of information:

How do Heat Pumps work?

Air Source Heat Pumps (ASHP);

  • An ASHP unit takes colder external air from the outside environment through an evaporator coil fixed on an outside wall of a building, before heating refrigerant gases and harnessing the heat through a heat exchanger

  • Using mains electricity, the heat pump boosts the heat from the air to the level needed by the heating system, heating water in a buffer tank.

  • The heating system is fed from the buffer tank.

Ground Source Heat Pump (GSHP);

  • A long loop of pipe, filled with a water and anti-freeze mix, is buried in the earth. Depending on available space it can be in a trench at least 1.5m deep or a borehole of between 60m and 120m deep.

  • The liquid in the ground loop absorbs heat from the ground, which is a stable 8-12 °C.

  • As it passes through an electrically powered heat pump, the absorbed heat is extracted and the liquid goes back into the underground loop.

  • Using mains electricity, the heat pump boosts the heat from the ground to the level required by the heating system.

  • The heating system is fed from the buffer tank.

Is a heat pump suitable for my home?

Heat pumps aren’t suitable for every home. A typical installation ranges from 6 to 12 kW in size and work best in well insulated buildings, an especially good choice in new builds.

To install a GSHP plenty of outside space is required for the ground loop pipework which is generally buried in trenches. Commonly, approximately twice the square meterage of the property is needed, allowing for 50 to 80m of pipe per kW or 10m of (coiled) pipe which extracts 15 watts of heat per square meter. GSHP trenches are commonly 1.2 metres deep.

Alternatively the pipework can also be inserted into boreholes which will extract around 50 watts of heat. In this case, suitable access is needed for drilling machinery.

Boreholes use less land, but are more expensive to drill. They tend to need between 20 and 50m of pipe per kW and more than one pipe can be put in each borehole. Boreholes are usually 100 – 150mm in diameter and up to 120m deep.

The geology of the ground around the property is important in determining whether a ground source heat pump is suitable. For example, sandy soil drains fast and does not hold heat well and as a result heat pumps will not perform well in an area with this soil composition.

An ASHP takes up much less space, but a distance of approximately 3 metres between the Heat Pump unit and your neighbour’s property is necessary to adhere to building regulations.

Due to their compact size, ASHP are ideal for use in flats and urban areas, particularly in places where there is no mains gas supply, or to replace electric heating. Noise from the fan must be below 42 decibels from a metre away to meet permitted development rules.

What can you earn?

Renewable Heat Incentive (RHI)

The RHI is a government funded scheme aimed at encouraging homeowners and landlords to make the switch from fossil fuels heating systems to a renewable heat solution.

Domestic RHI rates are:

Air Source Heat Pump: 7.42p per kWh
Ground Source Heat Pump: 19.1p per kWh
Payments are index-linked and paid quarterly in arrears for seven years.

The heat demand figure will be taken from the property’s Energy Performance Certificate (EPC).

Non-Domestic RHI rates are:

Air Source Heat Pump: 2.54p per kWh
Ground Source Heat Pump: 8.7p per kWh for first 1,313 hours per annum and 2.2p per kWh there after.
Payments are index-linked and paid quarterly in arrears for twenty years.

Payments are calculated by submitting quarterly Heat Meter reports to Ofgem.

To calculate the payments for a Domestic RHI application, follow the formula in this example:

House with a heat demand of 18,000kWh per year.

Installing an air source heat pump with an efficiency rate averaged over the whole year (seasonal performance factor – SPF) of 4 – 400% efficiency rating generating an average of 4kWh of heat for every 1kWh of electricity used.

Tariff rate (ASHP) of 7.42p per kWh.

The RHI is only paid on the renewable element of the heat, not the electricity used. To find that figure use the formula: 1 – 1/SPF

1 – 1/4 = 3/4 of the electricity will be counted as renewable.

18,000 x 3/4 = 13,500kWh x 0.0742p = £1001.70 per annum x 7 years = £7,011.90 total payments.

Fuel Cost Saving

In addition, you will make some savings on fuel costs.

  • 18,000 kWh of oil @ 5.36p (per kWh) = £964.80 (annual heating bill)

  • 18,000 kWh of LPG @ 8.32p = £1,497.60

  • 18,000 kWh of electricity @ 18.05p = £2,529.00

  • 18,000 kWh of mains gas @ 4.29p = £772.20

  • 4,500 kWh of electric for ASHP @ 18.05p = £812.25

(Source for Fuel Prices – Correct as of June 2015:

Find out how you could benefit from a Renewable Heat Solution.

Contact Blake Ecotec on 0333 600 56 57 or email


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