A group of 6 ‘heat pump curious’ visitors, organised through our local climate group, cycled from Woodchester to Nailsworth to visit our heat pump and get their questions answered. My wife took some videos of me extemporising. It was a cold day (about 6C outside).
The house is over 200 years old, Grade 2 Listed, and with a floor area of about 250 square metres. Instead of having one large heat pump, Cotswold Energy Group, who installed the system 3 years ago, provided two smaller units. This had the benefit that for much of the year only one is running, as was the case on this visit (if, as one of the visitors pointed out, it had been -6C, then both would have been in operation).
Explaining the heat pump in plain English
So here is the first of the short videos – a plain English short talk (11 mins) explaining how a heat pump works and answering their questions.
You will notice that at one point I had to crouch down to see if one or both units was running – rather demonstrating the low level of noise they produce. At another point in the video, some of the visitors had to shuffle sideways as they were experiencing the cold air from the heat pump (which extracts heat from the air, as explained in the video). I also mention a figure of 20 litres of water a minute as the rate of flow through the radiators. This was illustrative only and not a fixed number, as it depends on a number of factors, and may have been more than that on this occasion.
Explaining why underfloor heating is not required, using a simple model
In this video (2 mins) I explained how radiators can deliver the same heat as underfloor heating, by using a simple paper model for explanation.
Everyone commented on how cosy the room was. We looked at a thermometer that showed it was at 21C. I then got someone to put their hand on the radiator and I asked if they thought it was on, and they weren’t sure. I used a thermometer gun to see how hot it was – its was only 30C. Then I got them to turn their hand palm upwards and found the temperature was 28C, and so of course the radiator didn’t feel “hot”. But, it doesn’t need to be 60C, or 70C, to heat the room, just greater than the target temperature (21C) and sufficiently higher than that to deliver the heat at the rate that balances the rate at which heat is lost from the wals etc.
The flow temperature was a bit higher than this (as this was the surface temperature of just one radiator), but it illustrates the point. ‘Low and slow’ heating works, and delivers greater comfort.
Explaining why the bills don’t need to rise going from an old boiler to a heat pump
In this video, I used simple maths to show why a heat pump shouldn’t raise electricity bills even in an old house (if properly installed), and even with our high UK electricity prices.
I slightly rushed the last part on the relative costs explanation. In the 3 bed semi example, I needed 4,000kWh of electricity say at 28p/kWh totalling £1,120/yr to run the heat pump. Assuming a 70% eff. oil gas boiler we’d would need to consume 17,143 TWh of gas to deliver 12,000 kWh of heat (as 70% of 17,143 equals 12,000). So I’d pay 17,143 kWh x 7p/kWh = £1,200 with the old gas boiler, and that is a little but more than with the heat pump.
As the ratio of the electricity unit price to the gas unit price comes down, as it assuredly will, the economic advantage of moving to a heat pump will only grow (let alone all the other ones: massive carbon emission reductions; more comfortable home; independent of petro-states for energy needs, as grid itself is increasingly dearbonised).
Postscript
The organiser of the visit, Sylvia, sent me a lovely message afterwards:
“Hi Richard, just wanted to thank you for a really interesting tour yesterday… It’s so generous of you to share your home and your experience like that, we were all impressed at how well it was working in a house like yours. Shows how much bad info there is around! You did a good job of explaining some difficult concepts too! I think we all came away inspired… Even though we may not be able to make the change at once… So many thanks from us all!”
I really enjoyed the experience too, with so many great questions.
Thank you Sylvia for organising this.
Richard Erskine, © 2025
NOTES
- A question came up about microbore and I gave a reasonable answer I felt, but Heat Geek provides an expert explanation of the issues and potential solutions here > https://www.heatgeek.com/what-to-do-with-microbore-pipework-on-heat-pumps/ and whether you are heat pump curious home owner, but especially a heating engineer, Heat Geek will have answers to most of your questions, and also provides training and support for those in the industry wishing to move from gas boilers into heat pumps.
- For a detailed write-up of our heat pump project, see this essay here > https://essaysconcerning.com/2023/03/29/heating-a-listed-cotswold-stone-building-with-an-air-source-heat-pump-our-journey/
- For detailed calculations on the costs of running our heat pump in 2024, showing a modest saving compared to if we’d stayed with our old gas boiler, go here > https://essaysconcerning.com/2025/01/06/saving-money-with-an-air-source-heat-pump-in-an-old-house-2024-report/
- It’s worth noting that NESTA provide a ‘Visit A Heat Pump’ scheme that connects those like me willing to host house visits, and those who would like to hear from someone who has a heat pump. I have hosted visits using this scheme and will do more, but its also nice to use local networks to organise visits e.g. through climate groups, churches, Rotary, or whoever.
Technical Note
- For a deep dive on how radiators deliver their heat, an scientific explanation is provided in Using Radiators with Heat Pumps by Michael de Podesta.
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