We Are On Mains Gas: Should We Bother With A Renewable Heating System?

With a massive 83% of UK homes (21 million) on mains gas and the increased uptake of renewable technologies such as air source heat pumps, more and more people are asking whether there is any advantage to switching.

This week we hope to clarify some of the key advantages so you can make your mind up.

Heating And Hot Water Modifications

Once of the less-trivial aspects of switching to a heat pump system is that of the likely requirement to change radiators, or add an underfloor heating system, to ensure that the lower flow temperature in the renewable system will sufficiently heat the home.

Radiators can either be changed to larger or more efficient products or a new wet low temperature underfloor heating system installed if appropriate. Many wrongly conclude that an existing underfloor heating system for a boiler is the same for a heat pump and does not need to be changed. In fact this is false in the vast majority of cases. The pipe spacing will likely be too wide leading to cold rooms in the winter if connected to a heat pump system.

The hot water cylinder in the home will also have to be changed to a specialist product to cope with the lower flow temperatures from the heat pump too. These tanks will often have twice the internal coil than gas boiler systems.

Initial Cost

It is well understood that the cost of installing heat pump technology is indeed more expensive than a standard replacement gas boiler and indeed with the above home modifications this all adds to the total cost of change. Whereas it might cost around £2,000 to replace a boiler is may cost nearer £8,000 to install an air source heat pump and new hot water cylinder.

Running Costs

Seasonal costs for the two different heating systems, particularly for heat pumps are particularly dependent on heating design temperature and hot water storage temperatures.

The lower the flow temperature of the heating system the more efficient a heat pump becomes and indeed the lower the hot water storage temperature the less electric immersion has to be used to reach the required peak hot water temperature.

In fact if an air source heat pump system is installed with a really well designed underfloor heating system and the occupants are happy to have hot water stored at 50C then the running costs of the system could be 15% lower than that of an equivalent gas system.

Conversely an air source heat pump system run at 55C to heat a poorly designed emitter system and a hot water tank kept at 60C could use 20% more energy than a gas system.


The real benefit at present for heat pump systems, unlike fossil fuel gas systems is that they attract the renewable heat incentive (RHI); a 7-year tax-free government subsidy.

An average 3-bed semi with an air source heat pump installed could see around £900-£1,000 paid annually to help transition to low carbon heating. Even assuming no running cost saving this subsidy could help pay in full for the extra capital outlay within 7-10 years.

So there are a number of pros and cons for both fossil fuel and renewable systems when on mains gas fuel but done correctly and sourcing some up front capital, a renewable heating system may be just the right solution for you. It will be cheaper to run and attract government funds for a while to come.

If you would like to talk to a renewables expert about whether switching from mains gas to a renewable heating system is right for you. Contact me for a consultation.

photo credit: Rev.Dr.Seb via photopin cc

Doug Johnson

Doug is a chartered mechanical engineer and has had the pleasure of being involved in the UK renewable sector since 2008. With wide-ranging operational and design experience in both the domestic and commercial sectors across a wide range of recognised technologies he hopes to be able to share his experience to help enlighten and save you hassle along the way.