Domestic heating systems are responsible for around 14% of the total UK carbon emissions, due to their use of oil and gas to fuel them. Given the Government's determination to achieve net zero emissions by 2050 it is easy to understand why they are keen to see us rid ourselves of the sources of those emissions, namely our gas or oil fired boilers. On that basis, it has put in place a ban on all new fossil fuel gas boilers being installed in existing homes after 2035 or 2025 in the case of new build homes.

The strongly advocated alternative to a fossil fuelled central heating boiler appears to be an air source heat pump which is a reasonable alternative in a new build property, designed and build to accommodate a heat pump. Replacing a gas boiler with a heat pump in an existing property however, is not without its problems.

Making this transition is not just a simple swap out, there are practical issues which make the change over much more difficult. Gas combi-boilers, which are probably the favoured fossil fuelled boilers in many households, are simple to install. They take up relatively little room, don’t need a hot water tank and give us instant hot water on demand. Replacing a faulty one with another similar boiler is relatively simple. The new boiler can occupy the same position as the one it is replacing and is simply plumbed in to existing pipework connections. It utilises the same central heating radiators and continues to provide hot water when we require it.

An air source heat pump on the other hand does not store hot water or give it on demand, therefore it requires a hot water storage tank, which means it needs space in the property to house the tank. The heat pump itself is installed on or close to the outer wall of the property so does not need space inside but the space freed up by this, is not necessarily the best site for a hot water tank. Some installations will involve siting the hot water tank in an existing cupboard, which in many houses can be difficult as cupboard and storage space may well be at a premium, others will opt to install the tank in the attic.

Either way, replacing a combi boiler with an air source heat pump in an existing property is no simple task in comparison with a straight like for like replacement of a combi boiler. It is also true that an air source heat pump will not heat your water to as high a temperature as a combi boiler. This means that your radiators will lose some of their heat also therefore you may do well to look at increasing the size of the existing radiators in the main living areas of the house to achieve the same room temperature.

Cost is also a major factor in the equation. Replacing like for like, a new combi boiler will cost around £2,000 to £4,000 to buy and with little or no additional hardware required, the only other relatively small cost would be that of the installation.

On the other hand, replacing an existing combi boiler with an air source heat pump requires a great deal more installation work. Firstly the heat pump needs to be installed on or near to the outside wall of the property, rather than in the position of the old boiler. This will entail forming a solid base, such as concrete or slabs, for the unit to be sited on then drilling holes in the outer wall to accommodate the pipework from the heat pump. You will then need to find a site for the hot water tank which a combi boiler does not need. An air source heat pump can cost somewhere between £8,000 and £15,000 to buy and install. Installation costs depend on the size of the heat pump and the amount of extra installation work required.

To help offset the undoubtedly higher cost of installing a heat pump which is seen as a much lower carbon solution to heating our homes than a combi boiler, the Government has introduced the Boiler Upgrade Scheme. Under this scheme you may be eligible for a grant of £7,500. There are conditions attached to this grant which you will find detailed on https://www.gov.uk/apply-boiler-upgrade-scheme. For instance, your property must have a valid Energy Performance Certificate (EPC) with no outstanding recommendations for loft or cavity wall insulation.

Installing an air source heat pump in a new build property however, is a much different proposition. A new property can be designed to accommodate the new technology of a heat pump fired heating system, meaning that there is no need to undertake expensive reconfigurations of an existing system. The architect will make allowances for the siting of the heat pump outside the building and look for the best internal site for the hot water tank – very often in the attic. This is also a good time to look at reconfiguring the heating system to ensure the best use of the heat pump system.

An air source heat pump will not heat water to the same temperature as a gas fired boiler, therefore some thought needs to be given to making the best use of the heat generated by a heat pump. The easiest way to compensate for this reduction in temperature whilst maintaining the required room temperature is to allow the lower heat to radiate from a larger surface. This may be achieved by installing slightly larger radiators in the upstairs rooms of the house where temperatures are normally kept lower than in the main living areas on the ground floor. For ground floor areas, under floor heating works well with heat pumps, providing a uniform level of heating in every corner of each room. Heat at a lower temperature, over a larger area is more efficient and safer if there are young children in the household.

Even with the Boiler Upgrade grant of £7,500, a heat pump installation in an existing property costing between £8,000 and £15,000 may be unaffordable to many households. By comparison the lower cost of installation of the same system in a new build three bedroom house with an average cost of £283,700 would be almost unnoticeable to a new house buyer. On that basis it would seem sensible to see all new builds to have air source heat pumps installed.

Could we see all new builds with heat pumps and solar panels incorporated as part of the developer’s planning permission? This would potentially make what seems like a heavy financial burden on many people, a much more affordable solution.

If you are considering extending or altering your home, you may find some of these services useful: