How FGHR works
Even a modern condensing boiler loses usable heat in its flue gases. A flue gas heat recovery device — fitted above or integrated into the boiler — captures part of that heat and uses it to pre-warm incoming water, mainly benefiting domestic hot water production. The boiler then needs less gas to reach temperature, typically saving a few percent of annual gas use, most in homes with high hot water demand.
It’s passive in operation, compact, and best specified with the boiler rather than retrofitted.
In the SAP calculation
SAP recognises FGHR through improved water-heating efficiency, helping the DER for gas-heated dwellings at modest cost. It pairs naturally with WWHR — one recovers drain heat, the other flue heat.
The bigger picture
FGHR only applies to combustion boilers, so its future is bounded: the Future Homes Standard removes fossil-fuel heating from new homes from 2027, and heat pumps have no flue to recover from. For conversion or extension projects keeping gas in the meantime, it remains a worthwhile line in the SAP toolkit. Ask us whether it earns its place in yours.