Case Study 3 - 1950s Terraced House - 30F to a C - No Heating to Gas Boiler

At the time of writing the methodology for EPC assessments of existing dwellings is currently RDSAP 10. The EPC for this property was conducted under the previous methodology RDSAP 9.94. A significant methodology overhaul from RDSAP to the Home Energy Model (HEM) is proposed to start in 2026 and government consultations indicates EPC metrics and formats are likely to change in the near future. These factors will change approaches to EPC rating improvement in the future.

This is another 1950s 3-bed terraced house, of the same design as the ones featured in Case Study 1 and Case Study 2.

It's an auction property, and it stood out to me because it demonstrates how much impact the heating system of a property can have on the EPC rating.

This property currently has no heating system within it at all. There's no boiler, no radiators, no hot water cylinder, no heating of any kind. It's all been strippd out.

I've included it here to illustrate the really bad EPC rating it currently has (30F) and the massive improvement in EPC rating that is provided by just one Recommendation on the existing EPC certificate: Fitting a gas boiler heating system.

The house was prepared for sale, and to comply with current legislation had to have an EPC in place in order for it to be sold. This just happens to be the condition that the current owners, a local housing association, decided to leave it in at the time of that EPC assessment and subsequent sale.

Let's take a look at the Features List on the EPC:

Looking at the table above we can see:

• The walls are cavity walls with insulation that has been added since construction (there's no 'assumed' after the words 'filled cavity) - Its described as 'Average', but it's as good as this property can be without additional internal or external insulation
• 200mm of loft insulation - that's good
• Double glazed windows throughout - that' good
• Lighting - is very good with LED lights throughout

So all those items are looking really positive for the property.

What's left are the items related to heating which are all rated as Very Poor.

This is due to the RDSAP methodology introducing the worst case scenario that electric heaters will be used to provide the required space heating for the property and electric immersion heaters used in a hot water cylinder for water heating. Insulation appropriate to the ogirinal age of the building will also be assumed.

This type of assumption is a standard approach in energy assessments, including non-domestic (ie commercial) EPCs.

It is just this area of space heating and hot water heating that is bringing the EPC rating of this property down to a really low level - 30F.

Let's look at the Recommendations list:

(There are further recomendations but I have not included them here)

Ignore Step 1, the cost is very high and the physical effort required is significant for a small gain in EPC rating.

Look however at Step 2, and the gain from fitting a central heating system based around a gas condensing boiler.

There would provide a 41 SAP point improvement to the EPC rating.

In reality, you'd be looking at the top end of that cost estimate range (~£7,000 or more), and the 74C rating displayed for Step 2 does include the 3 SAP point improvement from Step 1 as well - EPC recommendations are applied accumulatively in the list. If you didn't carry out Step 1 then you'd have to remove at least 3 points from that 74C, possibly more, as the presence of Step 1 might have helped Step 2 achieve so well.

We have seen however in Case Study 1 and Case Study 2 that this design of house with a filled cavity wall is capable of a C band rating when fitted with a gas combi boiler system and all other features are in good order.

It's therefore likely that a condensing gas boiler on its own will still bring this particular property into the C band, particularly when a specific model of boiler is recorded in an assessment rather than default efficiencies being assumed via a generic heating code.

A quick note about that recommendation for the gas boiler: This is effectively a fuel switch for the main heating system, and this recommendation appears on this EPC because a mains gas meter was present at the property at the time of the EPC assessment.

Had that gas meter not been present then a recommendation for High Heat Retention Storage Heaters would have been listed instead.

The recommendation for the gas condensing boiler in this case is for a combi-boiler because there was no hot water cylinder present at the property at the time of the assessment.

This case study really illustrates how bad an EPC rating can be when peak rate electric heaters are used, and how much difference simply changing the main heating system can make to an EPC rating when all other aspects of a property are in order.

For further information take a look at our Heating Systems page.

For your own property, the change in values described above will be different. Only an EPC assessment, or simulation, run on your specific property by a local energy assessor will give you accurate figures in oder to make informed decisions.