Thinking of getting a heat pump? Don’t judge a building solely by its EPC rating, says CSE’s retrofit coordinator Steve Cole. Instead, consider a heat loss survey to measure your home’s energy efficiency and see if a heat pump could be suitable.

In this blog, we share a case study on a listed building in Bristol that did exactly this, with surprising results …

Testing a so-called hard to treat, old, leaky, inefficient, listed home

David’s listed cottage is one of the homes we tested for Bristol Heat Pump Ready. David wanted to find out if his home was suitable for an air-source heat pump. His aim is to reduce his carbon emissions, but he was concerned his old stone cottage might not be suitable. He was also worried a heat pump might increase his heating bills.

David’s home dates from 1790 and has uninsulated thick solid stone walls, an uninsulated floor, and original single glazed windows. Typically, an EPC rating would suggest a home like this performs poorly regarding energy efficiency.

This is because EPC calculations use Reduced Data Standard Assessment Procedure (RdSAP) which tends to underestimate the performance of the fabric in old buildings. We explain more about the EPC assessment procedure and why the assumptions can’t be replied on for heat pump suitability here…

Testing heat pump suitability in a listed building

Three tests were carried out at David’s home to figure out how much heat was escaping from the building. First, we conducted an airtightness test to look at air leakage – those pesky cold draughts.

Secondly, we did a thermal imaging assessment to identify areas where it gets especially cold or where there are thermal bridges. A thermal bridge is like a shortcut for heat to escape, bypassing insulation. Typical examples can be window frames or where the floor meets the wall.

Finally, we carried out an overnight heat loss test. This involved heating the home overnight, then using internal and external temperature sensors to measure how long it takes to cool back down again.

The results of the heat loss surveys

The results were surprising and encouraging. In contrast to what an EPC might say, the tests found David’s home was actually quite thermally efficient.

As the table below shows, David’s house performed better on the heat loss tests than a typical older home.

Type of building	Thermal efficiency rating (Heat Loss Parameter)
High quality house	0.5
Modern house	1.5
David’s house	1.75
Typical older house	2.0
Typical very old house	4.25

In theory it would be possible to install a 7kW heat pump to meet the existing heating demand. This would result in a £300 increase in David’s annual heating bill which is approximately £1,000.

However, with the data from the surveys and from working with David to understand his home, we’ve modelled that it might be possible to reduce this more.

This would involve some fairly simple improvements such as further draught-proofing or by adding shutters, secondary glazing, or thermal blinds or curtains on the single glazed windows. These measures could reduce the size of the heat pump and lower the increase in his yearly bills to only around £30 more than what he currently pays.

In this video, David explains what he learnt from his home heat loss survey.

https://www.youtube.com/watch?v=72NLh6QInF8

Is this historic listed building suitable for a heat pump?

The tests show a heat pump is viable in David’s home in the sense that it could meet his heating demand. Practically speaking, it’s viable too as he already has a hot water cylinder and the existing radiators are wide double panel and well-placed.

So, while some elements might need replacing, it might be possible to keep some of the old heating system and re-jig the radiators.

Because the building is listed, it’s unlikely the external unit for a heat pump could be fitted to the front of the property. Meanwhile, due to special limitations to the rear of the house it would have to be physically mounted to the rear walls. This would require consultation with a conservation officer and most probably listed building consent.

So we still need some further investigations. But we know a lot more about David’s home energy performance thanks to the testing.

As part of Bristol Heat Pump Ready, we’re piloting this approach to try and overcome some of the problems with incorrect heat pump installations and the assumptions about heat pump suitability in different types of home.

Accurate testing to measure the true heat loss of a building gives a much clearer picture of which homes are suitable for a heat pump. You might be surprised. Find out more about heat loss surveys here…

Bristol Heat Pump Ready

Bristol Heat Pump Ready is part of a national programme administered by the Department for Energy Security and Net Zero through the £1bn Net Zero Innovation Portfolio. Bristol Heat Pump Ready is an exciting collaboration between partners across the city. Together, we’re working to match the perfect heat pumps with the right homes. You can find out more here.

If you’re not in the target area for Bristol Heat Pump Ready but interested in a heat pump, you might be eligible for the Boiler Upgrade Scheme (BUS) to help fund it.