Summary

Heat pumps are recognised as the main alternative for gas boilers for providing heating and hot water in homes. There are two main types of heat pump – air source heat pump (ASHP) and ground source heat pump (GSHP).

Heat pumps work a bit like refrigerators, but in reverse, taking heat energy from external sources (e.g. from external air and from the ground via boreholes) and raising its temperature before transferring the heat to the central heating system to provide heating and hot water. Note – Heat pumps are not a direct alternative to combination (‘combi’) boilers as hot water storage must be introduced.

Heat pumps are powered by electricity (instead of gas) and are very efficient at generating heat. GSHPs are the most efficient but will require either digging up a large area of garden or drilling a deep borehole. ASHPs are easier to install and can be positioned discreetly (see Letchworth Design Principles requirements below). 

Heat pumps operate at lower temperatures and are well-suited to large heat emitters such as underfloor heating or conventional wet radiator systems. Heat pumps are a reliable, tried and tested technology but as with many retrofit measures, the system must be correctly designed, sized and installed to provide comfort and long- term financial benefits.

Heat pumps can be installed in most homes and it is not always necessary to fully insulate a home to make it ‘heat pump ready’ (However, there are a wide range of benefits of insulating, even thin layers – see IWI and EWI). Poorly insulated buildings would require a larger heat pump and larger radiators to operate efficiently. 

Cost/difficulty

MEDIUM/HIGH COST – Air source heat pumps cost around £14,000 and ground source heat pumps cost around £28,000 (Energy Saving Trust). GSHPs can cost double if a borehole is needed. There are grant schemes available which could reduce costs to below £10,000, depending on the work required.

MEDIUM DIFFICULTY – A typical MCS heat pump installation can take about 6 weeks from date of order to installation, and installation can take 4 or 5 days with 2-3 people working on it – The Surrey Home Energy Improvement Guide (2025), page 14.

Applicability in Letchworth

Applicable, subject to certain requirements being met. 

In regard to air source heat pumps (ASHP), the Heritage and Modern Character Area and Design Principles (DRAFT) state that:

Air source heat pumps (ASHPs) present an opportunity for residents to heat their homes with low carbon emissions. However, the installation of ASHPs can negatively impact residents, neighbouring properties and the street scene when not installed appropriately.

ASHPs will usually be approved providing that they adhere to the following guidelines:

• ASHPs must not detract from the character of the property
• Units must be designed and located in order to minimise the visual and noise impact from the property, neighbouring properties, and the street scene
• Units must be sited at the rear of the property, or potentially to the side where adequate screening from the street scene is already in-situ
• Units should preferably be mounted on the ground
• ASHPs must be sited a minimum distance of 1 metre from any boundary
• Secondary equipment such as external condensers, pipework and air conditioning units must be discreet, and must not be visible from the street
• We would discourage the installation of more than one ASHP at the property

We would encourage ASHPs to be considered when designing rear extensions to properties, provided they adhere to the above guidelines.

Whilst our consent is not required for internal alterations, please be aware that there may be internal considerations involved when considering the installation of an ASHP.

Insights from People Powered Retrofit

“Fitting a heat pump is one of the biggest changes you can make to reduce a home’s carbon emissions. It decarbonises space heating and hot water and removes one of the biggest uses of fossil fuel (gas) from a home. Our survey and retrofit options study of a typical home in Letchworth (see scenario 2 in this report) found that installing a heat pump would cost around £14.5k upfront and should cost about the same to run as heating a home with a gas boiler (but there may be opportunities for savings if some smart tariffs are used).”

Case study

Links to further information

• Energy Efficiency Guide for Letchworth Garden City residents (2024), page 6
• HCCSP Retrofitting Your House Guide (2024), page 25
• Saltaire Retrofit Handbook (2024), page 30
• Retrofitting Your Home – Cambridge Guide (2022), page 23
• The Surrey Home Energy Improvement Guide (2025), page 12

Image credits – Energy Saving Trust