FGHRS & WWHRS

At the time of writing, the methodology for EPC assessments of existing dwellings is RDSAP 9.94. This updates to RDSAP 10 on 15th June 2025 and a significant methodology overhaul from RDSAP to the Home Energy Model (HEM) is proposed for 2026. In addition, government consulations indicate future changes to the format of EPCs and minimum rating levels required for priate rental properties. Methods for improving EPC ratings may therefore change in the future.

This uses remaining heat in the exhaust gases passing through a boiler flue to heat up the incoming mains cold water, for domestic hot water, before it enters the boiler.

This results in the boiler using slightly less energy to heat the incoming water  to the required  temperture. 

As EPC ratings for domestic properties are currently based entirely on cost, this results in a slightly better EPC rating.  

Some boilers can have FGHRS built in, but it's more often seen as an additional device fitted above the boiler, in-line with the flue.

The presence of FGHRS can only be recorded in an EPC assessment if the device in the property is listed in the Product Characteristics Database (PCDB), hosted by the Building Research Establishment (BRE):

https://www.ncm-pcdb.org.uk/sap/searchpod.jsp?id=17

On their page, click on the 'Flue gas heat recovery sytsems' button to see the range of systems listed.

Flue Gas Heat Recovery Systems in domestic properties are pretty rare. Most people aren't aware of this type of system and it provides quite a low EPC rating improvement considering the expense of having one fitted.

Example picture here of an Alpha Gas Saver FGHRS:

For my 1950s terraced house that we cover in Case Study 2, this could provide me with an increase of 1 SAP point from 68D to 69C.

This is a small increase in rating, but it's another option that could be useful if like me, you are on the threshold of moving up a rating band.

Check the PCDB before purchasing a device, and also check with a local Energy Assessor to make sure the device makes a difference to the rating for your property before proceeding.

WWHRS is a heat exchanger that uses some of the heat from waste water exiting a bath or mixer shower, to heat up incoming cold water to a mixer shower.

This results in slightly less hot water being required by the mixer-shower to maintain the required shower temperature.     

In turn, because EPC ratings for domestic properties are entirely cost-based, this reaults in a slightly better EPC rating. 

There are at least three ways this device can be configured in a property, particularly in new-builds, but for my existing 1950s house the easiest way for me to retrofit this would be the type that sits directly under the bath and is self contained. This type is suitable for me because I have a mixer shower over my bath, and fitting other types would require a more costly and difficult installation.

WWHRS devices can only be recognised in an EPC assessment when fitted to a mixer shower.

If I was happy spending the money, I would look first at the Recoup Easyfit+ device. This costs around £600 for the device plus fitting. The cost per SAP points increase is relatively high but it's another option that could be useful if you are on the threshold of moving up a rating band.

For my 1950s terraced house that we cover in Case Study 2, this could provide me with an increase of 1 SAP point from 68D to 69C.

Example picture of the Recoup Easyfit+:

To be included in an EPC assessment, any WWHRS device you install must be listed in the Product Characteristics Database (PCDB), which is maintained by the Building Research Establishment (BRE).

Check the PCDB before purchasing a device, and also check with a local Energy Assessor to make sure the device makes a difference to the rating for your property before proceeding.

The PCDB is available to search here:

https://www.ncm-pcdb.org.uk/sap/searchpod.jsp?id=17

Click on the section for Waste 'Water Heat Recovery Systems' and view the list of devices.

Click here to return to our 'Improve Your EPC' main page, and see if there is another way you could improve your EPC rating.