Installing an Air Source Heat Pump

What is this Project About?

Some SusWoT members have been investigating the process of replacing your Gas Central Heating System with an Air Source Heat Pump. This is a big step that householders are now considering as a way of reducing their CO2 emissions.

The material that will appear on this page is still being developed and will be updated regularly. The technology is improving very rapidly, so what was not available a year ago may well be available now now. This is particulaly true of the heat pumps are they are a fairly new technology and there is huge investment to make the better. There are lots of things to consider when undertaking this changes such as the danger of causing problems with condensation when installing insulation or making decisions about things without consideration as to what the final set up should be.

In time we will add links and further information as to help you

Eliminating Gas Consumption in your Home – Heat Pump Installation


You may already have an EPC (Energy Performance Certificate) for your home. The EPC will give a general indication of energy efficiency but a more detailed assessment will be needed before you can plan specific improvements.

Ideally you should have a computer model which would replicate your existing heat loss and energy consumption. Various energy efficiency measures can be tested and the model could calculate the likely energy savings which could be achieved.

This may seem complicated but it is an essential step to finding the best method of bringing your property up to the standard which would allow for an efficient heat pump installation. Money spent on a full survey at an early stage can avoid the risk of embarking on expensive work which may not be appropriate for your property. You may also need the full survey if you want to apply for a grant.

Improvements to Thermal Efficiency

Loft Insulation.

Ensure that your Loft Insulation is optimum depth.

Depth of insulation will usually exceed depth of ceiling joist therefore you may have to install a walkway to ensure safe access across the loft area.

The loft must have adequate ventilation to minimise the risk of condensation.

Electrical wiring may need to be re-routed so that cables and junction boxes can be located easily. There is a risk of heat build-up if cables are covered by a thick layer of insulation. Must be accessible and safe.

Wall insulation

External Insulation is likely to be most effective.

May change external appearance of the house

No disruption to interior

Brickwork acts as thermal store.

Internal Insulation.

Loss of internal space

Disruption to interior

Potential problems due to trapped moisture between the insulation and surface (cold) of the brickwork/old wall plaster.

Heat Pumps

Details of how a heat pump works can be found on line. Technology has developed considerably in recent years and equipment has become more efficient. We are reaching a point where a heat pump can be a cost effective replacement for a gas boiler. However you do need to consider all of the issues before embarking on a heat pump installation.

Many heat pumps may operate at lower temperatures than gas boilers.

May require larger radiators.

Often recommended for use with underfloor heating system.

Consider extra cost of larger radiators etc. and disruption to the house.

A recently developed heat pump system is designed to operate at higher temperatures (similar temperature to gas system).

This new system may eliminate the need for larger radiators but it will require a large storage tank. The size and weight of this tank suggests that it will have to be installed on the ground floor.


Replacement of a gas boiler with a heat pump may not show significant cost savings especially if you have a fairly new and efficient gas boiler at present. If you are replacing an older boiler the potential savings will be much better.

The most important issue to bear in mind is that, within the next few years, gas prices will rise substantially compared to electricity. Government policy is aimed at phasing out gas as a fuel. The heat pump cost savings will become more apparent as fuel pricing policies kick in.


  • Survey and energy modelling
  • Loft insulation
  • Wall insulation
  • Heat pump installation to replace gas boiler.

Further Information links

Centre for Sustainable Energy

Futureproof Project.

January 2022