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Why you should measure heat loss before choosing a heat pump

Thermal image of a house showing heat loss from the walls
13 September 2023

An EPC rating doesn’t tell you everything. To know exactly how energy efficient a house is, you need to delve a little deeper.

Measuring your home heat loss will help you understand if a heat pump can work in your home. A home heat loss survey will also give you useful information about what to prioritise to improve your home energy efficiency.

Why measure heat loss?

Lots of people are interested in replacing their gas boilers with heat pumps to try and help tackle climate change and rising energy costs. As more people get heat pumps installed, the price will continue to go down, and they’ll become more accessible for more people. Eventually all future heating systems will need to be from low carbon sources.

If you buy a home, or rent one, it should come with an Energy Performance Certificate (EPC) rating. This ranges from A-G depending on how energy efficient it is. A being excellent, G being not very good at all.

EPCs include an estimate of how much the home energy bills are, but it’s all based on assumptions. They aren’t usually reliable when it comes to precisely knowing how much heat a building loses or how much your energy bill is.

Heat loss assumptions

EPCs use a process called Reduced Data Standard Assessment Procedure (RDSAP), where desk-based calculations are made using assumptions about the performance of the building’s fabric. This includes the roof, walls and floor and services such as heating and hot water.

The traditional method of sizing a heating system makes the same assumptions to estimate heat loss from each room of a home. These are used to calculate what size the various elements like the heat source, radiators and pipes need to be.

So, both these assessment tools use assumptions to estimate how quickly a room or whole building loses heat. One of the problems is that no consideration is made of the condition of a building. This means people may end up with an incorrectly sized, inefficient heating system.

For example, if a home is damp or in need of some repair – both things which increase heat loss – this won’t be taken into account.

This hasn’t always been a big problem. When these assumptions are used to install gas boilers for example, even with badly sized and arranged pipes and radiators, a boiler can usually still provide enough heat, albeit inefficiently.

The goldilocks porridge of heat pump installation

However, there is much less room for error when dealing with lower temperature heating systems like a heat pump. We need to get the system design just right, like the porridge from Goldilocks and the three bears.

If a heat pump design is too small, the home will not get enough heat. Too big and you’ll be fitting something much more expensive than needed. If your heat pump is not set-up correctly, it could end up costing far more than your old heating system to run.

How do you know if a heat pump is suitable for your home?

To match the perfect heat pumps with the right homes and increase the accuracy of calculating heat loss in a building, precise tests have been developed to measure the actual heat loss of a building. This removes the guess work when sizing a heat pump.

At CSE, as part of the Bristol Heat Pump Ready project, we’re working with Veritherm and Build Test Solutions, market leaders in the surveying industry to deliver these tests.

Bristol Heat Pump Ready: the heat loss survey

Home heat loss calculations

So, how is heat loss measured? A rapid overnight test is carried out that essentially heats up your property overnight. Then internal and external temperature sensors measure how long it takes to cool back down again.

No one can be in the property when this is happening – the home must be completely ‘at rest’. If this is not possible, a longer, three-week test is available. It uses similar data but requires additional information from your energy meters and the property can remain occupied.

Bristol Heat Pump Ready is piloting this approach to try and overcome some problems with incorrect heat pump installations.

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! 

For example, we’re working with David who lives in a listed building dating back to the 17th century, and his home heat loss survey revealed a heat pump could be an effective home heating option.

How useful is a home heat loss survey?

Measuring your home heat loss can give very useful information about your home. It can give you a clear list of priorities to make energy efficient home improvements. And give you some ideas about whether a heat pump could work for your home. By measuring first, before making any decisions about heat pump suitability, you can take out some of the guesswork.

So don’t assume your building isn’t suitable for a heat pump; get a measured heat loss survey to help inform you.

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