Heat Pumps

Air Source or Ground Source?

Air source and ground source heat pumps work in slightly different ways, and each have their merits. The type of heat pump that is best for your property depends on a number of factors such as cost, space and efficiency. Both are very efficient, with two thirds of the energy required to power the heat pump taken from the ambient ground or air heat which is both renewable and free of charge. The remainder is provided from mains electricity or from on site renewable electricity sources such as solar PV.

Ground source heat pumps have many advantages, despite being more expensive than air source heat pumps:

  1. -Ground source heat pumps have a higher seasonal efficiency, as the temperature of the ground remains constant, and the temperature of the air fluctuates
  2. -They are 125% more efficient than air source
  3. -They are very quiet
  4. -The units tend to be smaller
  5. -They attract a higher rate with the Renewable Heat Incentive, paid at 20.89p vs 10.71p for air source

However, air source heat pumps have advantages over ground source for a number of reasons:

  1. -Air source heat pumps do not require extensive drilling or ground works
  2. -If you do not have a lot of outside space, air source heat pumps are discrete and easy to install at your property
  3. -Air source heat pumps are considerably less expensive than ground source. An air source heat pump install costs between £9,000-£14,000, whilst a ground source heat pump install costs between £10,000-£18,000, but can be more depending on the ground works required.
  4. -An air source heat pump install takes 2-3 days, whereas a ground source heat pump install can take much longer
  5. -Air source heat pumps are still incredibly efficient, and achieve warm temperatures at -15° and below

The difference in compensation from the Renewable heat Incentive is quite high, and goes some way to recuperating the cost of your heat pump.

How do Air Source Heat Pumps work?

A heat pump system is comprised of three main parts:

-The heat source itself: air and electricity supplied by mains or a renewable source
-The heat pump unit
-The heat distribution system

Sunlight Future recommends the highly efficient Stiebel Eltron heat pumps

A refrigerant liquid with an extremely low boiling point is passed through a coil that is exposed to the outside air or to underground pipes. Even on a cold day the heat of the ambient air causes the liquid to boil and become a low-temperature, low-pressure gas. This gas is then compressed, which causes it to release the heat and turn back to a liquid. The heat is transferred to water in a heating circuit, which is used to run radiators, underfloor heating systems and provide hot water. The liquid repeats the cycle and the heat transfer process begins again. The process is shown very clearly in the video below from the Energy Saving Trust:

How do Ground Source Heat Pumps work?

Ground source heat pumps work by drilling boreholes into the ground, deep enough that the temperature remains stable all year. Fluid is passed through the pipes, and picks up heat from the ground. This is then compressed to agitate the molecules and heat the liquid, which is passed through the heating system, warming your home. There are several ways a ground source heat pump can be installed, one of which is shown another Energy Saving Trust video below:


Unlike the video above which shows a large ground loop, boreholes are now thought to be more efficient. Boreholes drill deeper vertically, rather than using up a large surface area for shallow pipes. The benefit of this, is that even with limited outdoor space, a ground source heat pump is still a possibility.

What do you need?

  • -An outside area, and permission to carry out ground works
  • -A space for the unit outside
  • -A space for a water tank

The images below show the two types of ground source heat pump. On the left, you have the ground loop and on the right you have the borehole.

Is my home suitable?

The vast majority of homes are suitable for Heat Pumps, and only in very rare cases is planning permission required. When we talk to you, we will ask you the following questions:

  • Do you have an up to date EPC?

    We ask this because if you have had an extension built, or changed your insulation, your old EPC will not reflect the heating needs of your property. MCS recommends that you renew your EPC every 2 years. If you do not have an EPC or are unsure about whether you should renew it, talk to us and we can assist you. If you are developing a new-build property, we will use your SAP calculations to make your quote. Contact us for further information about installing heat pumps on new properties.

  • How many bathrooms do you have?

    We ask this because it will affect the size of the water tank your system will require. We might also use the number of people in your property to help us calculate this.

  • Do you have space for a water tank?

    A heat pump system requires a water tank in order to provide you with hot water. Tanks can be floor or wall mounted, and typically require a space slightly larger than a regular water tank. If you are unsure whether you can fit a water tank in your property, talk to us and we can assist you.

  • Do you have space for a heat pump?

    Typically this isn't an issue for most people. A heat pump looks similar to an air conditioning unit and sits on the outside wall of your property. Many people position them on the back or side of their house. Before you contact us, think about where your heat pump might go and we can advise you if it sounds like a good location.

  • What is your home insulation like?

    We will ask you whether your home is well insulated. If you are in a newer property, your home is likely to be well insulated. Those in older, more rural properties may need to consider floor, roof, and external wall insulation before getting a heat pump, if your property does not have it. If you are unsure whether your property is insulated, contact us and we will advise you.

  • What kind of heat emitters do you have?

    Most homes have radiators as their main heat emitter. We will ask you how old your radiators are: radiators that were installed after 2000 are considered modern as they have a flow temperature of 50 degrees. Radiators older than that might not have a high enough flow temperature, and we may recommend that you upgrade them to help the efficiency of your heat pump system. Underfloor heating is the most efficient way of heating your home, and if it is possible for you, where possible we recommend using underfloor heating to heat your home with a heat pump however modern heat pumps can work with regular radiators, the heat loss calculations we produce of your property will allow efficiencies and running costs to be calculated.

Financial incentives for renewable heating (RHI)

Heat pumps qualify for the government’s Renewable Heat Incentive (RHI) which pays you for the heat you produce over the first 7 years of the system life – more than recovering the cost of investment. Heat pumps are more expensive to install than a gas or oil boiler but gas/oil boilers never recoup their initial cost and will be increasingly more expensive to run.

The RHI was increased in September 2017 from 7.63p/kWh to 10.18/kWh (20.89/kWh for ground source) so for a house using 12,500 kWh/year with an air source heat pump, a payment of £1272.50p will be generated.

Click for the official Government RHI calculator for England and Wales

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