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Low Carbon Living: Installing and running an air source heat pump

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Local Wigginton resident, David, shares his experience of purchasing, installing and running an air source heat pump

David Wilde, March 2023

An air source heat pump (ASHP) is a great choice if you want to dramatically reduce your home’s carbon footprint! However, it is important to do some research before making a decision to find out whether it would be a good fit for your home. From installation costs to making sure your heating system can support an ASHP, here are a few key tips from my experience installing one in my home.

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David's ASHP
"Viessmann (16kw output)"

Product specifications

Date installed: October 2021

House type: 4-bed detached

Installation cost: £15,000

Maintenance costs: £360 p/a (incl. 7 year warranty)

Electricity usage:

  • Starting up: 4.5kw

  • Running: 2-3kw (average)

Carbon footprint (home + water heating): reduced by around 50%

Air source heat pump_David Wilde.jpg
Article: Installing and running an air source heat pump: About Me

How does it work?

An air source heat pump works similar to a refrigerator (or an air conditioner) but in reverse. A fridge pumps heat from its cold interior to the warmer air outside, an ASHP pumps heat from the outside air into the domestic heating system. Neither of these devices actually generates heat, although an ASHP certainly appears to - out of thin (sometimes very cold) air.

The Technical Stuff:

  • The heat output is between twice and four times greater than the power used by the machine. The ratio of the two is called the Coefficient of Performance (CoP).

  • The average CoP is hard to predict accurately because it depends on a lot of variables, especially the temperature difference between ambient air and heating system water. The smaller this temperature difference, the more efficient the system is and the higher the CoP. A typical value for the CoP would be about 3.

  • Flow temperatures can range from 35 to 50+ degrees C. A low flow temperature requires large radiators to transfer the same amount of heat as normal size radiators running at a high temperature. Underfloor heating is the optimum solution with an ASHP as it works with lower water temperatures.

Check out Energy Saving Trust's guide on air source heat pumps for more information.

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Sourcing an installer

When I got quotes, there was a shortage of experienced ASHP installers. Out of 4 quotes, two were clearly insufficiently experienced. For example, my installer was not good at providing paperwork (i.e. guidance on use, details of guarantee/maintenance) which is important as this helps you understand your ASHP better so that you can use it more effectively over a long period of time.


  • Get at least 3 quotes from different tenderers. Make sure they are experienced with this technology and before you sign a contract, get an itemized tender including design cost, written terms of guarantees on parts and labour, and details of the maintenance contract.

  • Make sure your installer is registered on the Microgeneration Certification Scheme – this is essential if you want to get the £5,000 Boiler Upgrade grant. Check or decide which make of heat pump you prefer and ask the manufacturer for a list of their approved, MCS certified installers.

  • Obtain references from local customers if you can!

Space and building requirements

ASHPs are not recommended for poorly insulated properties. Insulate the fabric of your building first (i.e. double-glazing, roof/wall insulation) and then consider heat pump options.

You will also need to:

  • Locate outside space for the air source heat pump

  • Locate inside space for a hot water tank (in my case, in place of the old one) and a buffer tank (in my case, where the gas boiler was).

  • Choose the least intrusive site for your ASHP and check that it will satisfy planning rules on noise and position (it is quiet but not silent to run)

  • Get an energy performance certificate (EPC) - to apply for the Boiler Upgrade Scheme (a grant of up to £5,000), you must have a valid EPC containing no recommendations for loft or cavity wall insulation.

Check out the Government website (click here) for more information about the Boiler Upgrade Scheme.

Article: Installing and running an air source heat pump: Text
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Carbon Footprint

My ASHP has reduced the carbon footprint of my home and water heating by around 50%. In time, I hope that the low carbon content of the national grid (ie wind/solar etc) will increase and my carbon footprint will reduce further.

Article: Installing and running an air source heat pump: Famous Quote

Running an air source heat pump

My ASHP was installed in October 2021. It uses about 4.5 kW when starting up and averages 2-3 kW when running normally. My flow temperature with enlarged radiators is set at 50 and it is sufficient, though we supplement it with our woodburner when it’s very cold. General advice for best efficiency is to run the ASHP at the lowest temperature possible. It is advised to run your ASHP all the time because stopping and starting wastes power. I am experimenting with this!


My ASHP cost about £15,000 (including installation) plus £2,000 to replace the radiators with larger ones. A heat pump requires maintenance so I also took a maintenance contract with the manufacturer for £360 per annum, which includes a 7 year warranty.

Government support

At the time, the Renewable Heat Incentive grant applied. This has since been replaced by the Boiler Upgrade Scheme which provides a lump sum of £5,000 to install a low-carbon heating systems such as an ASHP in place of existing gas or oil heating. Find out if you are eligible by checking out the Government website (click here).

Final thoughts

Not cheap to install and running costs are at present comparable to gas but could well reduce over time. For off-gas homes using oil, LPG or electric heating, an ASHP might already be cheaper. It works best if left on all (or most of) the time and is less efficient if you require a quick burst of heat.

Costs should be considerably less for a smaller property and a smaller machine. This was for a detached 4-bed house. I estimate that my ASHP costs are presently a few percent more than my gas boiler would have been. If electricity prices fall more than gas (or rise less!) then the ASHP may become the cheaper option.

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