Heat Pumps in Historic Buildings: Addressing Myths and Misconceptions

Dan: Good afternoon, everyone, and welcome to our latest webinar on the subject of heat pumps, which will focus on some of the common myths and misconceptions regarding this heating technology. My name's Dan McNaughton, and I'm a building services engineer at Historic England, and I'm joined today by Sehrish Wakil.
Sehrish: Thanks, Dan. Good afternoon, everyone. My name is Sehrish Wakil, and I'm also a building services engineer here at Historic England. And we're glad to have you all with us here today for this webinar. So, without further ado, we'll start off with the agenda for today's presentation. Firstly, will provide you with a brief recap on heat pumps following on from our previous technical Tuesdays. on heat pumps, where we've discussed heat pumps in more technical detail. Following on from that, we will dive into some of the reasons why we are focusing on the myths and misconceptions around heat pumps in today's webinar. Then, we will explore debunking some of the common myths and misconceptions around heat pumps that are found to come up time and time again. We will then round up with some top tips, where we will provide some practical insight and advice around heat pumps. And then, we will conclude this webinar with opening the floor to those of you tuning in for our question and answer session. So, before we dive in, we'd like to get a sense of your experience with heat pumps. Please take a moment to respond to the poll on your screen, where we've asked you, what is your experience with heat pumps? The options are, you're very knowledgeable and understand how they work and the benefits, or you may know the basics, but don't necessarily consider yourself an expert on them just yet. Or, you may have heard of them, but don't know too much about how they work. Or, you might not have any idea what a heat pump is, and you want to join this webinar to understand more about them.
Dan: Okay, thank you. That is… So, most of you have answered, quite a good spread, and hardly anyone saying that they're not sure exactly what a heat pump is, which is encouraging. But don't worry if you are that one person, you'll have a much better idea by the end of this session. I think the majority, though, is- hopefully you can say you're saying I know a little bit about them, but would perhaps like to know a bit more. So. Thank you, everyone. Thanks, Sehrish..
Sehrish: Thank you all for answering that poll. Really great to See what level of knowledge everyone has on heat pumps on this webinar. So, we'll start off with what a heat pump is. A heat pump is an electrically powered type of heating system that works much like a refrigerator or air conditioner, but it moves heat rather than creating it. There are various types of heat pumps, and depending on which type is being used, they can take heat from a variety of sources such as the air, ground, or water, and can transfer it where needed. Without getting too technical, they work by a compressor that moves a special fluid, which is known as a refrigerant, through a cycle to capture and release heat. Heat pumps deliver warmth through air ducts, radiators, or even underfloor heating, and can also provide hot water to buildings. Furthermore, heat pumps can also be combined with other heating plants such as gas, oil, or electric boilers in hybrid setups. In addition, many heat pumps can also work in reverse to cool your spaces in summer as well. For every unit of electricity used, a heat pump can generally produce several times more heat. For example, according to the International Energy Agency, a typical domestic heat pump floor home produces four times the energy it consumes, making it three to five times more efficient than a gas boiler. Typically, in an old building with historic construction, heat pumps can reach around 2.5 to 3.5 efficiency ratings. This process makes heat pumps much more efficient than traditional heating systems as a result, and thus use less energy, and help to reduce the carbon emissions produced as a result of your heating system.
Dan: So I'm going to explain why we chose to focus on myths and misconceptions today. But before I do that, we would really like to know what myths or misconceptions you may have heard. So, if you could type what you've heard into this word cloud, which Matt is going to help us with, and we look forward to having a look at what you have to share. If you can respond in one or two key words, that is great. Just thinking that this is a word cloud. But the challenge I want set is to use no more than five words, please. Yeah, we’re definitely covering some of those today. The noise is featuring quite big. That's something I'm going to talk about in a bit. And there’s so many of you typing, it's actually quite hard to read it. Sehrish: I can see one of the bigger ones is that they're expensive to run. So, that's something that I'll also be touching on later on in this presentation. Yeah, good stuff.
Sehrish: Yeah. Brilliant.
Dan: I think we can have a job capturing this one. I’d quite like to get a screenshot of this. A few people saying they don't work in older buildings. We can help with that. And yeah, I think… Matt, are you okay to capture that at some point? Because it looks like people are really going for it with this word cloud. Okay. Well, let's move on now anyway. I think we'll leave it there, Matt, if I can get the slides back. Thank you. Brilliant. So, choosing myths and misconceptions regarding heat pumps- and thank you, everyone. You have some brilliant ideas there. Clearly you've experienced quite a lot, as we have. As the focus today, choosing that myths and misconceptions focus made sense because I think that misinformation can be a significant barrier to the decarbonization of heating. And when I'm talking about misinformation, this is relevant for all buildings, actually, both modern and traditional. So, as well as hearing a lot of myths and misconceptions firsthand, I want to share this media article from 2023. And this was genuinely the first article that I came across when I did a search for an article on heat pumps. I'll give you a moment just to have a read of this yourselves, and actually to focus on the highlighted words. So, given that the average member of the public will not have much knowledge about heat pumps, how likely is it that they would invest thousands of pounds in installing this heating technology if their only source of information is this article, which uses language such as “who will save our ears? Homeowners fume, noisy droning contraptions, costly heat pumps, at the behest of the government,” implying that it has been forced onto the public. And nobody really likes being told what to do. and “making their lives hell.” Now, I can think of two reasons why someone would spread this type of negative misinformation. The first reason is being misinformed, and actually we've all got a role to play in educating these people. But the second reason is more deliberate, and I want to share a bit about what was found to be happening in 2023. So, it's been widely reported in Energy Trade Association, that, no surprise, represents and promotes gas boilers and manufacturers, was behind a barrage of negative press attack on heat pumps. A PR agency employed by this association generated two thirds of the high profile negative content published about heat pumps between 2021 and 2023. And hopefully you can begin to understand why Historic England are keen to dispel as much of the common myths and misconceptions as possible, because heat pumps are vital to the decarbonization of heating in the UK. And the government is also making efforts to try and dispel this misinformation, as reported at the start of 2025. But, in amongst the misinformation, there's also been some really positive information and news about heat pumps published, such as this user survey of over two and a half thousand domestic heat pump owners. The report was published in 2023 and we will put a link to it in the chat. And the key findings of this report are that heat pump users are highly satisfied with the heat pumps, considering them to be safe, reliable, quiet heat sources that are effective for space heating and producing hot water. Overall satisfaction levels between heat pump and gas boiler users are very similar. Compared to the previous heating system, 73% of heat pump owners are as satisfied or more satisfied with a heat pump, which is excellent news. And this finding was particularly interesting for us at Historic England, in that there was no evidence that user satisfaction with heat pumps compared to their previous heating system differed according to the age of people's home. This suggests that heat pumps are likely to be effective across the range of residential property types.
Sehrish: Thanks, Dan.. That was really interesting, and it was really interesting to see some of those new articles digging into some of the misconceptions around heat pumps. So, now we'll come to this part of the presentation, but we'll dive into some of the more common misconceptions that we've heard around heat pumps. To start off with, our first misconception is, heat pumps don't work when the weather is cold. This isn't true. According to the Energy Saving Trust, most current heat pump models work fine down to about -25 degrees Celsius. Some advanced cold climate heat pumps have actually been designed to work in temperatures even as low as -35 degrees Celsius. If we look at this graph developed by the Carbon Brief that compares the average temperature of European countries in January, it gets the percentages of homes that have had heat pumps installed irrespective of the associated country. And we can see that the highest percentage of heat pump installations in homes in Europe can be found in some of the coldest climates. As we can see here in the bottom right corner of this graph, the four countries with the largest share of heat pumps installed in households are Norway, with 60% of its households having heat pumps installed, followed on by Sweden, with 43% of its households, then Finland with 41% of its households, and Estonia with 34% of its households. Furthermore, as can be seen on the graph, these four countries also face the coldest winters in Europe heading into the minus degree temperatures, which range from around -4 to -9 degrees Celsius. Whereas compared to the UK, where on average we face temperatures of around five degrees Celsius in January, we have a much lower percentage of heat pump installations in our homes.
Dan: Yeah, and I think it should inspire confidence with heat pump technology, knowing that over 60% of homes in Norway have heat pumps, despite this being one of Europe's coldest countries. So, the next misconception is that heat pumps don't work with historic or older buildings. And that one definitely came up in the word cloud earlier. I know this isn't true because I’ve designed heat pumps that work well in listed buildings. And you've probably already guessed that the wide range of older buildings that are shown on the slide all have heat pump installations. And to learn more about all types of heat pumps in historic buildings, we've carried out four investigations solutions, which in total included 14 air source heat pump case studies, five ground source heat pump case studies, and five water source heat pump case studies. And the first investigation was published in May 2023. We'll put a link to it in the chat for you. Now, one of the key findings from our investigation was that air source heat pumps work well in a range of different historic building types and uses. And this is a good point in the webinar to share a film that Historic England have made, taking a behind the scenes look at an air source heat pump and solar panel installation in a Victorian terraced home. Again we’ll put a link to the film in the chat, and is well worth a watch. And please feel free to share this film if you'd like to, so that the message from Historic England will reach more people, and that message is that heat pumps can work well with older buildings.
Sehrish: Thanks, Dan. So, now we'll move on to the next misconception, that heat pumps don't work if you don't improve the thermal properties of the building's fabric itself first. By building fabric, we mean the properties of your building, such as your window insulation, which refers to your glazing, such as double glazing or triple glazing, or other aspects such as your roof insulation or floor insulation. A heat pump will heat a building regardless of the condition of the fabric of the physical building itself, much like a gas boiler. However, improving the condition of a physical building can greatly improve the energy efficiency of the heating system and can reduce your costs, as well as the carbon footprint you produce as a result of the amount of energy used as a result of this. Nevertheless, as this graph developed by the International Energy Agency shows, heat pumps still use significantly less energy when compared to a gas spoiler. when heating an uninsulated home. And as we see here, the energy demand required for these heating systems to work drops further depending on the level of insulation in the building.
Dan: And then, we have the misconception that heat pump efficiency does not increase if you don't improve the fabric. I will admit that when we first covered heat pump misconceptions in our 2022 webinar, we correctly said that the efficiency of the heat pump depends on the external temperature, the system flow temperature, the choice of refrigerant and the manufacturer. However, what we didn't acknowledge was that if you improve the thermal performance of the building fabric, then you will need less heat. And most heat pumps will automatically reduce their flow temperature to account for the lower amount of heat that is required. And the important thing to understand with that is that lower flow temperatures result in higher heat pump efficiency. So, it just goes to show that we're always improving our understanding of heat pumps, and that you can actually improve the efficiency of your heat pump by improving the thermal performance of your building fabric. And of course, higher efficiency results in lower running costs and lower operational carbon emissions.
Sehrish: Thanks, Dan. The next misconception is around heat pumps being a relatively new technology. Well, as this timeline developed by the Regulatory Assistance Project shows, this isn't quite the case. Heat pumps have a long history, dating back to the 1850s, when Lord Kelvin and Peter von Rittinger first explored the principles. The first working model was built somewhere between the years 1855 and 1857. But it wasn't until the early 20th century that heat pump technology gained traction with the development of early refrigeration systems. In 1937, one of the earliest water sourced heat pumps was installed in Zurich City Hall, where it provided heating for decades. The 1940s and 1950s saw the rise of ground source heat pumps with documented installations in North America and Europe. By the 1970s, the oil crisis drove interest in energy efficient alternatives, leading to further heat pump adoption. In the 80s and 90s, manufacturers focused on improving cold climate performance. Advances in technology such as reversing valves, variable speed compressors, and enhanced vapor induction allowed heat pumps to operate effectively in subzero temperatures. This ushered in an era of highly efficient variable capacity heat pumps. Today, heat pumps can operate in extreme cold, as mentioned earlier, with some models performing efficiently at low temperatures. As mentioned previously, some models have efficiency ratings nearing 400%. As a result, they can provide a sustainable alternative to traditional heating systems.
Dan: Thanks, Sehrish. I really love the graphic on that last slide, and how it quite simply just shows the history of heat pumps. It's really good. So, moving on, I find the misconception that heat pumps are too noisy to be an interesting one. And it was one of the bigger contributions from viewing the word cloud earlier. So, hopefully this will be of interest to you. So, in my own design experience, I have had to design very expensive acoustic enclosures for heat pumps as shown on the right. And the reason that I've had to do this was to satisfy very stringent acoustic planning conditions for a listed building located in a dense urban area. So, when it came to investigating heat pump installations with Historic England, part of the investigation was deliberately focused on noise mitigation measures and the end users’ experience with noise. What really surprised me was that out of the 24 case studies, only one of them had any acoustic mitigation measures installed. Noise was not an issue at any of the installations. The image on the left shows the one case study where there was an acoustic louver installed to the front elevation of a dry, stonewalled heat pump enclosure. If you get a chance to read the report which we mentioned and shared in the chat earlier, you will see that we're not convinced that the acoustic louver was actually needed. Whilst it won't do any harm, we realized that the heat pump was only providing heating and not domestic hot water. So, during the warmer weather, when the picnic area that you can see is more likely to be used, the heat pump won't actually be operating.
Sehrish: Thanks, Dan. That was really interesting, especially to understand the effect of noise on the pumps. So, on to the next misconception, heat pumps can only provide low flow temperatures. Well, let's start off with traditional gas boilers. They tend to have a flow temperature of around 60 to 80 degrees Celsius. And so, your radiators at this temperature can feel very hot to the touch if they're fueled by gas. However, with a heat pump, the flow temperature is generally lower, and at around 35 to 55 degrees Celsius. So, your radiators are super warm enough to heat your building but won't feel as hot as they do with a traditional gas boiler. This lower temperature means that you may need to increase the size of some of your radiators to ensure that they can deliver the heat to your home at the right rates. The lower flow temperature means that your heat pump works At a greater energy efficiency when compared to a gas boiler. It can therefore result in lower carbon emissions.
Dan: So, heat pumps heat building slower than gas boilers is one of the more common misconceptions. And it's actually only true in a retrofit project if you don't consider the existing radiators, pipework and pump. For example, a radiator designed to provide one kilowatt of heat, a typical boiler flow temperature of 80 degrees C will provide exactly the same amount Of heat as a radiator designed to provide one kilowatt of heat at a typical heat pump flow temperature of 40 degrees C. The only difference will be the size and form of the radiator. But that doesn't always mean that radiators installed to work with heat pumps have to be triple-panel radiators with a large depth, which is something which you see quite common in proposals. To illustrate this, I've shown images of a radiator that I've sized to work with a heat pump and the existing radiator that was replaced. Overall, the length and height of the radiators was similar, and the only difference in this case was that I went from a single-panel radiator to a single-panel radiator with fins on the back. Hopefully this demonstrates one of the benefits of getting good technical advice when considering options for your heat emitters.
Sehrish: So, the next misconception, which is that heat pumps are too expensive and they can't achieve financial payback, is a topic that is widely discussed at the moment. There is not any certainty around the future of electricity prices. This line graph, developed by NESTA, shows the difference in how much the average home would need to pay per year for a heat pump compared to a gas boiler from the year 2000 to 2035 In two different scenarios, one being the baseline, when nothing changes and stays as is, currently equal electricity prices, the other being a cheaper electricity scenario, which takes into account future policies and possible subsidies. At current energy prices, running costs for heat pumps are around the same as for a new gas boiler. The baseline scenario starts around a breakeven, which is approximately a negligible difference of £0, and shows a steep increase to £670 in 2028. This then decreases slowly to £510. What we find by looking at this data is, if the imbalance in gas and electricity prices is addressed, heat pumps are thought to become the cheapest way to heat your home. But as we mentioned previously, if you are replacing an older boiler, heat pumps can be cheaper to run. If the heat pump is installed and used properly, it can run even more efficiently and can potentially work in lowering your heating bills further.
Dan: Thanks, Sehrish. The last misconception that we're going to share today is that heat pumps need to be conceal or or screened for esthetic reasons. So, both water source and ground source heat pumps are actually installed in internal plant rooms, which means we're only considering air source heat pumps with this misconception. And again, our investigations of 14 air source heat pump case studies in older buildings showed that they didn't need any visual screening. The image on the left shows the design of an enclosure that I've designed to visually and acoustically screen a heat pump installation. There was no planning requirement to provide any visual screening, but it's worthwhile pointing out that this was a £5 million domestic retrofit project, which had a landscape architect and a really nice garden. So, what I'm trying to say is that this design wasn't your typical domestic heat pump installation. And on the right there is an example of digitally printed vinyl wraps that are available for heat pumps. They aren't cheap, and I don't have a strong opinion on these, but I would strongly advise that you should always check that it doesn't void the heat pump manufacturers warranty before considering something like this. And in July 2024, Historic England has produced a new advice note to provide clarity and support consistent decision making for proposals to reduce carbon emissions and improve the energy efficiency of historic buildings. And this includes advice relating to heat pumps. Again, we'll put a link to this advice note in the chat for you. So, there is a lot of heat pump advice that we could talk about. I think we could do a whole webinar on it, actually. So, I’ve tried to pick out a few tips that I think will be the most useful for you when considering a heat pump installation as part of a retrofit project in an older building, And the first one is aimed at those buildings that are listed or in a conservation area, and that is to try and engage with your local authority as early as possible. In my experience, this gives the local authority the opportunity to provide any planning conditions early in the project. And the other bit of advice that I would offer is to be positive and objective in your communications, which I know can be challenging, and be prepared to adapt your proposals where required. Where there are concerns from the local authority, it's best to try and understand the concerns as much as possible because this will give you the best chance of designing a solution. The next hot tip is that heat pumps should never, ever be sized on a like for like basis in terms of their heating capacity when compared with the boiler that is being replaced. Quite a lot of reasons for this. And as an example, last year at my home — that's my heat pump you can see now hopefully — I replaced a 28 kilowatt gas boiler with a seven kilowatt air source heat pump. And if you take one thing away from today, this is the one top tip that I would encourage you to remember. And those of you that have experience with heat pumps, and I could see from the poll there's quite a bit of understanding, so quite a lot of you worked with one or own one already, this next- advice about not replacing like for like might seem really obvious to you, but I recently saw a kilowatt heat pump installation where this is exactly what has happened. Next, finding a reputable heat pump installer can be a bit of a minefield. And I would say this is the most common question that I am asked about, which is how to find a good installer. And I always recommend asking the following questions. First, I want to know what experience you have with installing this technology in similar buildings, and are there any satisfied customers that you could speak with? Second, can you talk me through how you demonstrate the operation and optimization of the heat pump to your clients? And what I mean with optimization is basically configuring the heat pump to work most efficiently. It's really important if you're gonna have a successful project. What actual energy performance have you achieved with your installations? And with that question, look for specific values for energy in kilowatt hours or percentage improvements. I'm really interested in what coefficient of performance or efficiency that their installations typically achieve. You're going to need at least 2.5 for air source heat pumps, or at least 3.5 for ground and water source heat pumps, and preferably higher. I want to know what calculations that they perform to assess the compatibility of existing heat emitters, distribution pipework, and pumps. And I also want to know how you determine if the property has sufficient electrical capacity. I want to know what post-completion visits you carry out to check that the heat pump is performing as intended. And finally, it’s always a good idea to find out if the installer will offer a servicing contract, because that can take the stress away from trying to find someone to maintain this plant in the future. And get a quotation, find out how much that servicing contract would be. And if at any point you get a vague or defensive or unconvincing response, then I'd seriously recommend looking elsewhere. Then, a final top tip is to speak with your network and your contacts to try and visit successful heat pump installations in buildings that are similar to your own building in terms of size, construction type and age. And this might sound obvious, but go on a cold day so that you can experience the heating firsthand. What you will learn could be invaluable to your decision making. And if you're finding it difficult to find a heat pump to visit, Sehrish found this website which is conveniently named heatpump.com. It's quite catchy. And we'll put a link to this in the chat.
Sehrish: Thanks, Dan. That was really useful, and it gave a really good overview of what 58,01, to do when you're thinking about getting a heat pump installed. To follow on from that, our team has another upcoming Technical Tuesday webinar on the 29th of April at 1pm on the subject… Sorry, on the 8th of April at 1 p.m. on the subject of heat pumps, and we would love to hear your ideas about what the focus should be. We are going to put up another word cloud, and we would greatly appreciate it if you could type your ideas and suggestions around what you would like to hear more around the topic of heat pumps, with two or three key words. Then we will have a look into this and see what we can do. Well, I think the biggest one was case studies.
Dan: Churches are quite prominent in there as well, so you would be quite interested in my other work which looked at decarbonization of heating in churches as well. Because what we found in that was that air source heat pumps were the preferred recommendation in about a third of the cases. So, thank you, everyone. Lots of ideas there. I think Sehrish and I are gonna be quite busy planning The next one.
Sehrish: We definitely will be. We’ve got some great suggestions.
Dan: Thank you, everyone.
Sehrish: Fabulous. Thank you for answering that word cloud. So, for more information about heat pumps and historic buildings and some of our guidance around installing heat pumps in historic buildings, please refer to our web pages and guidance notes around these topics. We will also post a link in the chat to our previous Technical Tuesday webinars, for those interested, where the buildings seen here at Historic England dives into more detail and all things heat pumps. The links will be posted in the chat. Thank you all for listening. Our email addresses are on the screen, and will also be posted in the chat, and we have some time for questions now.
Matt: Brilliant. Okay, Sehrish and Dan, thank you so much. Let's go into the Q&A. So, please if you could turn on your webcams so we can put a face to the name. That's absolutely fantastic. Dan, I noticed we had a lot of questions coming in the questions for the presenters chat. So, I've actually brought that into center stage so you can scroll through them and hopefully cherry pick the ones that you want to answer. Clearly we won't have time to answer all of them. If that's not working for you, Dan, I can lose it.
Dan: That's alright. I’ll pick two out, Matt, And the first one's a nice easy one actually. So, I just need to find it again. Okay. So, the first question, I think the very first one which came in, it says, when does Historic England expect the change in permitted development rights for locating heat pumps within one meter of the boundary? Well, I've got great news for you, that person. It’s already came in. It came in November. It's good news, actually. I've got mixed feelings myself because my heat pump went up- was installed in October 24, and I would have loved it to be right on the property boundary. So, I missed that by a month, as it turns out. But that's a good question to start with, and hopefully you'll be quite pleased with that news. And I'll answer one more. This again was one of the earlier questions which came in. The question says, is the pricing of electricity based on market value of gas, which is a bit of an issue when you start understanding energy supply, is that affecting uptake of air source heat pumps or any heat pumps? And will this method of pricing be changed? Well, I'm really hopeful that it will be changed. At the moment, We pay climate change levies on our fuel for gas and electricity, and for quite some time… When you understand how the national grid has been generating electricity and the fuel mix, you will see that the carbon content of grid electricity has been decreasing massively, certainly over the 20 or so years that I've been an engineer, and it’s really positive. But what hasn't been adjusted is the climate change levy apportioned to electricity. So, actually, that proportion of your fuel cost is disproportionately high, and there has been pressure and a lot of discussion about readdressing that so that those levies reflect the environmental impact. And unfortunately there isn’t a timeframe, which is one of those questions asked. Is it affecting uptake? I think it's got to affect uptake, because when you look at our uptake in the UK compared to the rest of the Europe, we are way behind the curve in terms of uptake, and if you can- if government are able to readdress the climate change levy afforded to gas and electricity, that means that you're going to go from air source heat pump installations costing approximately the same to heat your home as a gas boiler to it being cheaper. And then you've got that incentive to invest. And don't forget the 7500-pound boiler upgrade scheme incentive, which I took advantage of last year, is a game changer for me, and you don't have to pay any of that back. So, yeah, thank you. Thank you very much. Sehrish, have you spotted any questions yet?
Sehrish: I just wanted to follow one. in terms of the electricity prices. I've just posted a link in the chat with regards to the Clean Power Act that's been passed in the past months, and that just outlines the government's plans to decarbonize our electricity and energy usage. So, I would really recommend having a read through that to understand where we're at in terms of wanting to reduce our carbon emissions when it comes to our electricity usage as well.
Dan: Okay. I'm going to take another question just because it's staring me in the face. It says, does the two and a half to three times efficiency apply to when it's minus two degrees C outside? So, that's COP efficiency at two and a half to three. What actually happens is the efficiency of your heat pump drops off as it gets colder outside, but I will say share design data, and it varies across the UK. So, I'm going to specifically talk about design data for where I live in Wiltshire, and actually it doesn't really get to -2 degrees C, I think 99% of the year, it's at -2 C or above. So, we're talking about a tiny little fraction overall where that efficiency isn't ideal. And what you should be looking at isn't the instantaneous efficiency all the time, but you should be getting what's called a seasonal COP, or a seasonal efficiency from your manufacturer, because that will give you an average of how that heat pump will perform over the year. Sehrish, have you spotted any that you fancy?
Sehrish: We keep getting questions coming through.
Dan: I've got another one ready then, I'll let you have a read while I answer this one. So this one says, how can we keep using historic radiators where they need to be kept? Great question. And it does happen. I've seen entire stately homes keep all of their radiators, And actually, in one of earlier webinars, and I believe it was the water source heat pump one, we actually made a point of showing a radiator, a beautiful radiator in my eyes that was 100 years old, and it being connected up and was running really well, and doing a great job. In practice, what I tend to do, because when you can- contractors especially get a bit nervous with this in terms of liability and damage to the system. There can be a bit of nervousness about the condition of the radiators internally, are they going to be prone to leak, and there can be nervousness sometimes about, will any debris in an older system damage my heat pump if I'm spending thousands of pounds on that. So, there's a couple of things you can do to overcome them. I mean, I tend to specify that the radiators are cleaned inside and out. I also do a pressure test, which typically, when you're doing a heating system, you pressure test systems maybe two or three times, the system pressure, to make sure that it's not going to leak, so that you're not putting in older radiators which can be more sensitive to pressure damage and undue risk. I tend to reduce that down to about one and a half times systems pressure, which I find tends to work. Because you can have a real problem trying to get spare parts for older radiators if they leak or anything like that. Well, I think the last thing I want to say on that is, when you get your experienced heating engineers, they're actually able to estimate how much Heat output you might get from different radiator forms. So, that can be quite useful at the design stage, in the feasibility stage of a project, when you're trying to work out, will this radiator give you enough heat? There's actually a foolproof way of testing it. If you've got a system on a gas boiler or an oil boiler, just turn your flow temperature on your boiler down to 55 degrees C or 50 degrees C, try and do it when it's cold and see how those those radiators in those spaces perform, which is exactly what's happened in some large projects.
Sehrish: I finally found a few questions myself, managed to get the chat to freeze a bit. So, one question is, do you find it challenging to address deeply ingrained misconceptions and situations like a brief decarbonization report or consultation? How would you approach changing the minds of those who are firmly convinced that these ideas are wrong? I think it can be challenging at times, especially when people have very fixed And rigid misconceptions around heat pumps in general. I think a really good way to get around that and to convince people of, and as we're doing here, trying to bust some of the misconceptions around heat pumps, is really looking to existing case studies, showing clients, for example, of cases where heat pumps do work. For example, as we mentioned earlier, you know, there's that there's a huge misconception that you can't work in cold weather, when in fact a lot of countries that, you know, are pulling in the minus degrees are still able to utilize heat pumps effectively, and a majority of the households do actually actively utilize that. So really, I feel just proving it through case studies helps quite a bit. And then another question I found is, any examples of heat networks based on heat pumps? There are quite a few, especially within London as well. So this limited council is coming to mind right now. They have a whole new heat network system set up. I'd be happy to share a few links once I get to them, in the chat, providing use cases of them. But it's quite a good heat network. And just on that topic, I highly recommend hooking up to one if you have one that's accessible to you.
Dan: I’ve got a really technical question. It says Dan, was that your cat in the photo? Yes. Yes, it was. But I don't think that's what everyone's tuned in to find out. Actually, I might be wrong, So, really good question here. It says, with buildings in occasional Use, are air source heat pump still worth it? Are they too slow to bring the space up to the appropriate heat? So, there's a couple of parts to that question. The first part to that question, are they worth it? They might well not be, if I'm totally honest. What you've got to look at in any feasibility study, it doesn't matter if it's heat pumps or electric boilers or whatever it is, you're thinking, you've got to understand how your building's used as part of that feasibility study. You've got to understand the type of use, how frequently it's used, you know, who's using it. All of those are good questions. And when you understand that from the client, from the building owner, you can carry out the calculations to work out how much a heat pump is going to cost to run, and if there is any payback or financial consideration with that. But there's not- I wouldn't say there's a general rule. What I found out when I was looking at church building case studies is that actually heat pumps weren't worth it in some circumstances. And I'm talking about cases where the church was used once every three weeks on a Sunday, and you couldn't justify the capital expenditure for an infrequently used building like that. But it does vary on a case by case basis, so it's well worth looking into before you get too far in your project. And the other one talked about it being too slow to bring the space up to the appropriate heat. And I thought we covered that in one of the misconceptions I talked about, almost forget about the plan and whether the heat pump or the boiler is fast enough. It's all about your heat emitters. Are they sized correctly? Because sized correctly they can bring- that is what brings the space up to temperature, not the plant that’s powering all those heat emitters of various forms. So, hopefully that's helpful for you.
Sehrish: We’ve had another question come through. Can a heat pump be used to recover waste heat from inside a building? Yes, you actually can. You can use what's known as a heat recovery system. And it's a very efficient way to make the most of the energy that you would otherwise lose as a result of the system. And how it works is, a heat recovery system captures the waste heat from your heat pump, and it can then expect that waste heat from various sources inside your building such as your ventilation systems. If you’re not looking at domestic, Let's say you have a server room in your building, you could also look at utilizing the heat that's emitted from there, and you can then use this to again, it will heat up to- again heat, your building. So, yes, you absolutely can.
Dan: Lots of good questions to choose from. I think we're spoiled today. I'm going to take one about domestic hot water and air source heat pumps. What do you tend to specify? What's the best approach? Full disclosure, I don't do much design anymore, but I'm well aware of what is happening with domestic hot water and air source heat pumps. So, the last part of the question goes on to explain, says that the operational temperature of a typical heat pump is usually below the temperature required to kill Legionella, which is absolutely right. That fact is absolutely right. Well, I would say I mean, my heat pump, I'll explain how my heat pump works. I'm just sticking with a domestic example. So, my heat pump is capable of supplying a flow temperature of up to 55 degrees C, which is pretty good, actually. Whereas to kill legionella, to stall- and I do have a water cylinder as well. So periodically I should take that cylinder temperature up to 60 degrees C. So, there's a question, how do I get it from 55 degrees C to 60 degrees C, and in my case, there's an electric element inside the water cylinder that just bridges that gap. It doesn't do the whole cylinder up to 60 C, it uses the really efficient heat pump to take the cylinder temperature up to 55, and then the immersion, electrical immersion element, which is more expensive to run as well, just as that little bit of a top up. But there are actually so many different types of heat pump. I mean, there are actually heat pumps which can quite comfortably deliver temperatures up to 90 degrees C. So, it all depends on your project. And actually what I've seen on larger projects, if you're interested in this topic, is that they'll have a heat pump just doing the heating system, which might have a flow temperature a bit lower, say 40 degrees or 45 degrees C, to maximize efficiency and reduce running costs. But to solve the hot water problem, they might have a dedicated Heat pump that's just designed to do the hot water so that you're not compromising efficiency on the heating system. So, lots of different options there. And in really low use, just a bit of hand washing, you can use local electric point of use water heaters. So, it all depends on your project really.
Sehrish: Yeah. I've got another question. Do you think the challenges we are experiencing today with the transition from gas to heat pumps are comparable to those faced during the shift from oil to gas in the 1950s and 1960s? I think that's a really interesting comparison, and I think that there definitely are some similarities between the two situations. I would say that there is a lot around it as well that makes a situation a lot more complex than it was back then. For one thing, we have quite a few more buildings to heat than we did back then, so the switch from gas to electricity can be slightly more complicated in that regard, when you consider having to consider the grid’s resilience, for example, that's one key element. Another key element is, when we're looking at different buildings, you know, although we're promoting heat pumps, it's not always a one size fits all option. I think that's one key thing we want to make clear here. You know, you have to consider different factors and elements when you are sizing your heat pumps and looking at going fully electric. So, I guess to answer that question, in some ways, yes, but in some ways, I would say it's far more complicated than we let on.
Dan: Thank you, Sehrish. So much to read here. Just trying to pick out. We got a couple of minutes left here.
Sehrish: I found one. hydrogen gas powered heat pumps.
Dan: Go for it.
Sehrish: This is a really nice question. I recently got to attend a conference on hydrogen. So, the Climate Change Committee released a report a few weeks ago that essentially stated that hydrogen may not be the most suitable fuel to heat buildings domestically. The government still has yet to comment on this. And we will be expecting an update to the report in 2026. However, there has been a debate so far, which is hydrogen versus heat pumps. The general consensus at the moment is it would cost a lot to be able to generate enough hydrogen to fuel the whole economy within the UK. And there are definitely plans going ahead to produce hydrogen, but how that progresses, we are yet to see. But I would say in general there is a huge, far larger push towards heat pumps and for people to consider those options, and for hydrogen to be used for more new taxations in the future.
Dan: Yeah, thanks. I think I'm going to finish off this just one last question. It's related to that one, and you've already shared some of your thoughts on it, and it's quite simply, what's your view on hydrogen? So, it's something we've been aware of for a couple of years really, and it's quite well known, certainly among engineers and designers that hydrogen is much more energy intensive as a fuel compared with heat pumps. And what I mean by that is, it uses far more energy to generate and store hydrogen than it does to use that same energy in heat pumps. So, the government has, quite correctly, in my view, gone down and really pushed quite strongly for the use of heat pumps as its primary method of decarbonizing heating in the UK of it's not a one size fits all solution, and I'm actually quite interested in hydrogen just from the sort of technology side of things. But I do think it would be restricted to niche applications, industrial applications. So, that's my view on hydrogen, just to answer that one. And I think we will leave it there. We’re at 2 o'clock now. We’ll do our best to follow up with responses to as many questions as we possibly can. A massive thank you to you all really for joining us today. And if you keep an eye on the links And Historic England’s newsletter and website, we will make sure that we share the date of our next heat pump webinar. We look forward to it. Thank you very much.

[END]

Is the pricing of electricity based on market value of gas affecting uptake of air source heat pumps and will this method of pricing be changed?
I'm hopeful that it will be changed. At the moment, we pay climate change levies on fuel for gas and electricity. When you understand how the national grid has been generating electricity and the fuel mix, you will see that the carbon content of grid electricity has been decreasing massively, but the climate change levy apportioned to electricity hasn't been adjusted, making that proportion of your fuel cost disproportionately high. Recently there has been pressure and a lot of discussion about readdressing this.
Is it affecting uptake? I think it's got to - when you look at uptake in the UK compared to the rest of the Europe, we are way behind the curve. If government can readdress the climate change levy afforded to gas and electricity, that means that you're going to go from air source heat pump installations costing approximately the same to heat your home as a gas boiler to it being cheaper increasing incentive to invest.

Does the 2.5 to 3 times efficiency of heat pumps apply when it's -2 outside?
The efficiency of your heat pump does drop off as it gets colder outside, but it very rarely gets below -2⁰ in England, meaning that it is a tiny little fraction of the overall time where efficiency is affected. What you should be looking at from your manufacturer isn't the instantaneous efficiency all the time, but what's called a seasonal COP (or a seasonal efficiency), because that will give you an average of how that heat pump will perform over the year.

Can the ASHP unit be installed in a leaky outbuilding instead of directly outside?
When ASHPs are installed internally, there are specific ventilation requirements which must be provided. Unfortunately, these can’t be quantified by a ‘leaky outbuilding’ and each manufacturer has specific requirements for the designer/installer.

Do the higher flow heat pumps contain rather nasty but more effective refrigerants?
No, the opposite is generally true with natural refrigerants such as propane and carbon dioxide being common refrigerants in high temperature heat pumps. These refrigerants have very low global warming potential.

How can we keep using historic radiators where they need to be kept (LBs)?
It does happen - I've seen entire stately homes keep all their radiators. However, there can be concerns about the condition of the radiators internally, whether they are going to be prone to leaking, and whether any debris in an older system could damage the heat pump. In practice, what I [Dan McNaughton] tend to do is specify that the radiators are cleaned inside and out, and a pressure test is completed. Typically, you pressure test at two or three times the system pressure to make sure that it's not going to leak, however, to avoid putting older radiators at undue risk I tend to reduce that down to about one and a half times systems pressure.
Experienced heating engineers can estimate how much heat output you might get from different radiator forms and can be useful when working out whether existing historic radiators will give you enough heat, but there is a foolproof way of testing it yourself. Turn the flow temperature on your boiler down to 55⁰C/50⁰C when it's cold and see how your radiators perform.

Could a heat pump be installed inside a brick lean-to extension that originally had an outside WC?
Probably, not – it is unlikely to be large enough. Coincidentally, the video that we shared during the webinar shows a new heat pump being installed to the outside of this type of brick outhouse.

Do you have a guidance document on what to ask an installer?
Not yet, but we are thinking about adding a checklist to our webpages because we often get asked this. Our How to Find the Right Professional Help page may help when finding professional help and advice for historic buildings.

With buildings in occasional use are ASHP still worth it - or too slow to bring the space up to appropriate heat?
To answer the first part to that question, are they worth it? They might well not be. What you've got to look at in any feasibility study, whether it's heat pumps, electric boilers or anything else, is an understanding of how your building's used. You've got to understand the type of use, how frequently it's used, and who's using it to carry out the calculations to work out how much a heat pump is going to cost to run, and if there is any payback or financial consideration with that. There isn’t a general rule, and it varies on a case-by-case basis.
The second part of the question talks about heat pumps being too slow to bring the spaces up to the appropriate heat. You can almost forget about the plan and whether the heat pump or the boiler is fast enough, it's all about your heat emitters. Because, sized correctly, they are what brings the space up to temperature, not the plant that’s powering all those heat emitters of various forms.

Can a heat pump be used to recover waste heat from inside a building?
Yes, you can use what's known as a heat recovery system to capture the waste heat and make the most of the energy that you would otherwise lose as a result of the system. On a non-domestic level, let's say you have a server room in your building, you could also look at utilizing the heat that's emitted from there, and you can then use this to heat your building.

What about domestic hot water systems for air source heat pumps - what do you tend to specify as the operational temp of a typical heat pump is usually below the temp required to kill legionella?
The operational temperature of a typical heat pump is usually below the temperature required to kill Legionella. Sticking with a domestic example, my heat pump can supply a flow temperature of up to 55⁰C, whereas to kill legionella I [Dan McNaughton] should take that cylinder temperature up to 60⁰C. So, there's the question: how do I get it from 55⁰C to 60⁰C? In my case, there's an electric element inside my water cylinder that bridges that gap. The heat pump takes the cylinder temperature up to 55, and then electrical immersion element tops it up.
However, there are heat pumps which can quite comfortably deliver temperatures up to 90⁰C. What I've seen on larger projects is that they'll have a heat pump just doing the heating system, which might have a flow temperature a bit lower, say 40-45⁰C, in addition to a dedicated heat pump that's just designed to do the hot water so that you're not compromising the efficiency of the heating system.
In really low use hot water system, for example just a bit of hand washing, you can use local electric point of use water heaters. So, it all depends on your project really.

Can air source heat pumps be used with existing microbore pipework?
Occasionally, yes but in most cases the diameter of the pipework will need to be larger. This is because typically 2-4 times as much flow needs to travel through this pipe.

What's your view on hydrogen powered heat pumps?
The Climate Change Committee released a report a few weeks ago that essentially stated that hydrogen may not be the most suitable fuel to heat buildings domestically. The government is yet to comment on this and we are expecting an update to the report in 2026. The general consensus at the moment is it would cost a lot to be able to generate enough hydrogen to fuel the whole economy within the UK, and whilst there are definitely plans to produce hydrogen, we are yet to see how they will progress.
Hydrogen is also much more energy intensive compared with heat pumps. It uses far more energy to generate and store hydrogen than it does to use that same energy to power heat pumps.
In general there is a far greater push towards heat pumps as the primary method of decarbonizing heating in the UK.

What happens if there is an electricity cut?
Boilers require electricity to operate too, so for both boilers and heat pumps, there will be no heating until power is restored.