Low Carbon Living: Installing and running an air source heat pump
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.
"Viessmann (16kw output)"
Date installed: October 2021
House type: 4-bed detached
Installation cost: £15,000
Maintenance costs: £360 p/a (incl. 7 year warranty)
Starting up: 4.5kw
Running: 2-3kw (average)
Carbon footprint (home + water heating): reduced by around 50%
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.
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 mcscertified.com/find-an-installer/ 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.