Solid fuels: Biomass, wood burning stoves and open fires

Speaker: Dan McNaughton.

Dan McNaughton: Good afternoon, everyone!  

My name is Dan McNaughton, and I'm a building services engineer at Historic England. It's good to see some familiar names in the audience and lots of new names too, so thank you everyone for joining us today.  

This session is going to cover solid fuels, and if you have any questions today, please share them in the webinar chat, and I'll try and answer as many of those as possible at the end of the session. The main presentation will be recorded, as Matt said, for future reference and for sharing with your colleagues if you want to.  

So a little bit about me. In my design experience, I've designed large biomass systems, and I've done some interesting work with historic open fireplaces. And although a large part of my role at Historic England is providing technical advice on modern systems, I'm also interested in the history of building services and how we used to heat our older buildings before things like central heating systems and utility networks were in place. And I'll share some relevant history in the United Kingdom.  

So coal mining in the United Kingdom is understood to date back to Roman times, with coal being used in a variety of ways, including hypercore systems. And fire pits were used in the middle of a room in early buildings, and a hole in the ceiling allowed smoke to escape. Although the image shown is more of a fire than what I would call a fire pit.  

And close to where I grew up, actually, one of the earliest existing chimneys can be found at Conisbrough Castle in Yorkshire, and that date dates back to around 1185. Then after that time, fireplaces became more common, and the Franklin stove was created in 1740, and this was made of cast iron.  

And then from the early 19th century, homes in urban areas were supplied with town gas, which was produced by burning coal. So there's been a big change in how buildings have been heated over the past 1,000 years, and even a considerable change over the last century.  

And although we're just getting started today, there's something that I'd like to learn from you already. So we've got a bit of a poll, if we could put that one in please, Matt. And it's just to understand a bit more about you. So I just want to know, do you have a stove, an open fire, or biomass boiler at your home? And I'll just read out the possible responses. So yes, and I use it. Yes, but I don't use it. No, but I would like one, or no, and I don't want one. It's just to gauge where you are, really.  

So we've got a lot of you on the call today. We've got about 230 of you, so far, so that's really good. And most of you have responded already. And wow, we have got over half of our audience— I don't know if everyone can see the data, but that's around about 57-58%— 96 of you saying yes, you've got some former fuel-burning appliance at your home and you use it, which is just really interesting.  

So thanks for that, Matt! And if we'll move on. 

Matt Faber: We have a question, a quick question. Are you including log burners in this? 

Dan McNaughton: Absolutely. Absolutely. 

Matt Faber: So there you go. 

Dan McNaughton: Yeah. 

Matt Faber: So if it's a log burner, that's a yes. I'm guessing that you didn't expect that response. 

Dan McNaughton: Well, no, I mean, a log burner is what I'd call a stove, but perhaps a bit of definition would have helped there. But I'm waiting for this mass influx of log burners responding now, but we've actually got a very similar outcome. We've ended up with 56% saying yes, we've got something. So yeah, thanks for that. It gives me a feel for who we've got listening to today, and I think that'll have some impact on the questions a bit later, which is good.  

So, in this session, I'm going to cover the basics of how solid fuel burning appliances work. Then I'll spend a bit more time on the different considerations that you need to be aware of. I will say the case studies in this talk don't go into much detail, but it'll give you an idea of the kind of work that I get involved in with regards to solid fuels. But unusually, I'm going to start this session with a bit of a warning, and I think this is the only subject that I've ever done this with. So usually in our Technical Tuesday webinars, I provide technical advice and guidance on subjects like decarbonisation and best practice.  

But today I'm not going to try and persuade or dissuade you from using solid fuel burning appliances. And that's not just because I'm quite obviously outnumbered here today, but the reasons for that, in all seriousness, are because the use of stoves and open fires in particular are emotive subjects, and ultimately people like using them. Including myself actually, and a lot of people don't like to be told or advised about what they should or shouldn't do, especially when we're talking about appliances in their own home.  

So what I do want to do today is share what I know about solid fuels so that we can make more informed decisions. And there may be some points that are a bit hard-hitting, but I'll try and balance that with some of the positive things about this heating technology. So that's the serious message over with for now, and let's get going with something a bit more fun.  

So I want to share a bit about how and when I use stoves to keep warm, and the reason for the photos is to explain that I spend a lot of, a lot of time outdoors in the whitewater season, which runs from October through to about now, through to March time.  

And as part of this, I often stay over in some remote rural locations, and some of the places that I stay are so remote that they have well or spring water connections to the buildings. Many do have stoves or open fireplaces. And I can genuinely say that when you've been outdoors in the cold for large parts of the day, there is nothing, nothing nicer than relaxing by a fire. This particular stove was one that I used last month, and it made a huge difference one evening when a storm cut the power to the place where I was staying.  

And this— I think there's something that feels natural or primeval about burning things, keeping warm, and even cooking. I used to be a school teacher, and I remember doing a topic on prehistory and how much I and the children enjoyed cooking jacket potatoes around a bonfire on the school grounds. I'm not sure who enjoyed that more.  

But the other thing that I like about stoves like this one are how they provide a level of heating to adjacent rooms. When the fire is no longer burning, there is still that nice warm feel of residual heat that is still transferred to the building as the stove cools.  

So a quick word on radiant heat. And rather than going into the science of radiant heating, which is interesting, I just want to talk about how it feels. And what I'm about to say has some relevance for stoves and open fires. So when I'm explaining radiant heat, especially to someone who isn't technically minded, I like people to think about how the sun heats us. And our planet. And scientists will say that the sun is the primary source of all energy on Earth.  

But I want to talk more about the feeling you get when you are in direct sunlight, particularly on a cooler spring or autumn day when the air temperature may be lower at around 10 or 12 degrees C, but you can still feel relatively warm on a sunny and clear day because that radiant heat from the sun counters the cooler air temperature.  

And you can immediately feel that difference when a dense cloud stops the direct sunlight or you walk into a shaded area. And for me, that is one of the clearest examples of how radiant heat works. And stoves and fireplaces radiate heat in all directions by the same method of heat transfer, albeit at a much lower core temperature.  

So moving on, let's look at the basic science behind burning things. And the fire triangle, it might give you flashbacks to your school science lessons or maybe fire safety training at work, but the fundamentals are all there in that for something to burn, you need all three of oxygen, heat, and fuel. If you've had recent fire safety training, you may recall that there's now a fourth component and the triangle has now become a four-sided tetrahedron or pyramid with the addition of the chemical chain reaction as another important component.  

And the simple chemical equation— well, I call this one simple— on the right shows us that by burning the carbon in wood, coal, or other variants of these solid fuel products, we are essentially doing this to create heat with the byproducts of carbon dioxide, water vapour, and other products of combustion. When we think of chimneys or flues, we're often focused on them removing the dirty products of combustion, but they actually also help to remove the H2O, or water vapour, that could be detrimental to our older buildings.  

So we'll start looking at the practical considerations when using solid fuel burning appliances, and there is a lot to think about. Not surprisingly, whenever you burn anything, you will need a chimney or flue to convey the harmful products of combustion to outside. And when it comes to needing plant room space, that is an additional consideration for, for a floor-mounted biomass boiler. But obviously with stoves or fireplaces, they are located directly in the room that they are heating. And all three types of appliance will need a fuel store.  

However, this can be more of a consideration for biomass, particularly with larger boilers which may include automatic fuel delivery systems. The smaller biomass boilers have a hopper installed to feed the fuel, and it is important to appreciate that you need to be reasonably fit to be able to lift up a 15kg bag to fill a hopper. This is something to keep in mind if the occupier would struggle with this physical demand, and this has unfortunately happened where a biomass boiler has been installed but nobody at that organisation was physically able to refuel it. So it didn't get used. 

With all types of appliance, there is a choice of fuels. Biomass boilers typically use wood pellets or wood chip, which has a different moisture content, and the choice of fuel impacts the storage and delivery method of the system. The moisture content of the fuel affects the heat generated from the combustion process, and I'll talk more about the fuel choice for stoves and open fires a bit later.  

Regular maintenance and combustion air is required for all types of appliance. With stoves and fireplaces, there are minimum sizes of permanently open air vents that are required in the building regulations, and the size of these vents will depend on the size of the fireplace or the heating capacity of the stove. I've been involved in a project with historic fireplaces, and we did something clever using redundant soil pipes in a large stately home to provide the required ventilation for the open fire.  

The other experience I have with open fires is being involved in the design of a cast iron damper to close off a chimney when the fire is not in use to prevent cold downdrafts entering the building. It is of course very important to remember to open these before you next use the fire, although I'm sure you would quickly realise that mistake if you made it.  

Biomass boilers can be connected to conventional heat emitters such as radiators, underfloor heating, and fan convectors. And there is an increased risk of fire damage and carbon monoxide poisoning with stoves, and even more so with open fires, because these heating appliances are located within the living space. There is also occupier safety to consider in terms of the risk of burns, and even the surface temperatures of stoves can easily reach 150°C, so this is particularly important if there are vulnerable people living in the home.  

In terms of operating in off-grid locations, biomass boilers do need an electricity supply, whereas the other types of appliance obviously do not need this. And a final word on efficiencies: there isn't much difference between biomass and stoves because current eco-design stoves need to be at least 75% efficient. The main efficiency consideration to understand is that open fires are only around 25% efficient, with 75% of the generated heat being lost through the chimney. And to visualise what that means in practical terms, you could think that one lump of coal in a stove would provide around the same amount of heat as three lumps of coal in an open fire.  

So I want to share some information about permits and what you're allowed to do with different solid fuel burning appliances, and we'll start with biomass boilers. And this example is from a local authority, and they advise that biomass boilers are permitted development within existing dwellings, which essentially means that planning permission is not required. However, this does not apply generally to new-build homes, and there are rules for smaller biomass boilers which would be suitable for most homes, and the fuel and appliance have to meet the criteria required for use in smoke control areas. 

Moving on to stoves, we already mentioned that the more efficient eco-design stoves are the only type available to buy for a new stove installation. You'll need an exemption to burn wood in a designated smoke control area. In these areas, you'll only be authorised to burn smokeless fuels, and there is a note to advise that there is information in the building regulations about how to install the stove safely.  

On the subject of safe installation, you may have heard of HEATAS registered installers who are certified to install stoves, boilers, and biomass, and this includes chimney sweeps. Now, HEATAS is the Heating Equipment Testing and Approvals Scheme, and they don't just have registered installers, but they also have approved retailers. Without HEATAS certification, you have to contact your local building control to inspect and approve any new solid fuel installation.  

Now, the government website has information about smoke control areas and what you are permitted to burn. It also explains about financial penalties and fines if your chimney releases smoke in a smoke control area, or if you purchase unauthorised fuel to use in an appliance that's not approved by DEFRA.  

And this particular government website also has a lot of information about how best to use your open fire or stove, and that starts with just sensibly considering how often you need to use your solid fuel appliance and how much fuel you need to burn.  

The next two points relate to moisture content. They advise that what is called ready-to-burn fuel is a recognition of dry wood with low moisture content. Then explains how you can easily test the moisture content of freshly chopped wood using a moisture metre, and they're relatively inexpensive. They provide a list of approved solid fuels that produce less smoke, and they claim it can also be more efficient than coal. And there's also information about maintaining your appliance and the flue or chimney. They explain the benefits of eco-design stoves when compared with open fires, and finally, they mention the law relating to smoke control areas, which we've already had a quick look at.  

So, move on from the practical considerations and look at the environmental considerations. I'm going to start by talking about something which you may be familiar with already in terms of biomass, and that is the sustainability argument relating to the sequestration of carbon carbon dioxide. This really divides opinion, but quite simply, the idea is that the carbon dioxide emitted from burning biomass has already been absorbed by the plants during their growth.  

Therefore, the net carbon impact to the environment is argued to be zero. I understand that thinking and the thinking behind this, but I also know that biomass fuel is often consumed more quickly than new trees can be grown. There are some serious questions being asked about the source of the fuel.  

If it was that simple, and assuming that there was enough biomass fuel for everyone to burn, then we would have this technology in all of our buildings. But the reality regarding the impact on the environment is more far-reaching than just considering the carbon dioxide emitted to atmosphere.  

To appreciate the environmental and health impacts of burning different fuels, you need to understand the emissions from the combustion process. And the emissions include particulates of different sizes and chemicals that are known air pollutants. And when you understand these emissions, you will begin to appreciate why it really isn't the best idea to be burning things, particularly in our densely populated urban areas.  

This is the reason why many urban areas are only permitting the combustion of authorised fuels within smoke control zones. And to give you an idea of the scale of this, the blue area on the map is the smoke control area for the City of London. And I'm going to show you an enlarged view of this table on the next slide to explain these emissions.  

So this table considers the emissions that are produced for different fuels when 1 gigajoule of heat energy is used, and that's not an easy amount of energy to consider or talk about. So I'm going to tell you that this is approximately the amount of heat energy that the average UK home uses every week.  

And the top row of this table has been highlighted, and this shows the emissions when wood is used as a fuel. And I'll start on the left-hand side of this table with the pollutant PM2.5. And particulate matter of size PM2.5, which is recognised as the particulate size which can pass through our lungs and enter our bloodstream and cause health issues, has a diametre of 2.5 micrometres.  

If you aren't conversant with how big this is, a millimetre is 1,000 times shorter than a metre, and a micrometre is a million times shorter. And a natural gas-fired boiler will produce less than 0.1 grams of PM2.5, which is very low. However, an oil-fired boiler will produce 6 grams of PM2.5, which is at least 60 times more than the natural gas equivalent. And oil is often considered a dirty fuel. However, when we look at this, burning an equivalent amount of wood produces 375 grams of PM2.5, which is almost 4,000 times more than the natural gas equivalent.  

And moving along the table, the next air pollutant is black carbon or soot which is 22 grams for wood. And compare that with 0.25 grams when we burn oil, which is not the cleanest of fuels in itself. Now, black carbon causes diseases premature death, and it actually absorbs some sunlight heat in the atmosphere.  

Our next pollutants, our next air pollutants, are nitrogen oxides and sulfur dioxide. And actually, the levels of these pollutants in wood are higher, but I would say they're similar in value to what you find in oil. It's actually coal which is one of the worst producers of these pollutants. But what do they do? Well, nitrogen oxides cause smog, respiratory, respiratory issues, and together with sulfur dioxide, they acidify the rain, which can damage plants and wildlife.  

Moving on, the combustion of wood produces hundreds of times more CH4, or methane, than the other fuels, and methane is a significant greenhouse gas. And in 2021, it was reported that it forms ground-level ozone, which causes 1 million premature deaths worldwide every year.  

Wood also produces thousands of times more CO, or carbon monoxide, than other fuels, and this is involved in the production of ozone, which is a climate change gas. We then have polycyclic aromatic hydrocarbons, known as PAHs, which pose significant health risks linked to cancer. And unfortunately, these PAHs are 800 times more prevalent in wood than any of the other fuels, including oil, gas, or coal.  

And finally, when we burn wood, there are 18 times more non-methane volatile organic compounds than when we burn oil. These also cause ground-level ozone. So in conclusion, regardless of what you believe regarding carbon sequestration, there are significant environmental impacts when we burn wood.  

Now we've mentioned some of the health considerations already, but there is more that is worthwhile understanding. And I'm starting to notice more awareness in the media about the health concerns of solid fuel burning. Most of the media that I have seen has been focused on the restriction side of what we have already discussed. This is probably because this is a sensitive issue, and some people feel that this infringes upon their personal choices of how to heat their home. But I did see this recent article which reported the sobering news that in the UK, wood-burning stoves and open fires are linked to 2,500 deaths a year.  

And our universities are involved in researching the health impacts of solid fuel burning. University College London has recently reported findings linking wood burners to a decline in lung function. And this article from last month highlights that exposure to pollution can be an issue indoors when the home has a wood-burning stove.  

Now, the government have produced this graphic, which is quite easy to understand which again gives a visual representation of the amount of PM2.5 particulates in different fuels. So a little bit more engaging than the table that we saw. And starting from the left, the black emissions are from an open fire. Then we go from standard stoves to the eco-design stoves in yellow, and the PM2.5 emissions are similar for both the eco-design stove and pellet-fired biomass boilers before they drop significantly for oil-fired boilers shown in grey.  

And so far I've talked about the size of PM2.5 particulates without really explaining what they can do to us. And this is not a particularly pleasant graphic, but it does show how particulates of this size and smaller can be absorbed into our bloodstreams. Unfortunately, this is linked to serious health conditions such as heart and respiratory diseases, and there have been scientific studies on this subject.  

And this particular study from the University of Sheffield in 2020 really opened my eyes to the health risks of using stoves. The key findings of the study were that the occupiers were exposed to very high levels of particulate matter, PM2.5, during and following periods when lighting and refuelling the stoves.  

To share some data on the findings, the World Health Organization recommends that people are not exposed to more than an average of 25 micrograms per cubic metre of the particulate matter PM2.5 over a 24-hour period. What this study found was that indoor concentrations of PM2.5 range from between 27 and 195 micrograms per metre cubed on average over the period in which the stoves were used. To summarise, I think there is more that needs to be done to understand the health risks of using solid fuel burning appliances and more done to educate the general public as well.  

Now obviously it's quite hard-hitting when we talk about the environmental and health considerations of burning solid fuels. And I've deliberately chosen this image to convey some positivity, even though Christmas might be a distant memory.  

And on that positive note, I wanted to share where I think these appliances can work well. So rural locations lend themselves more to this type of heating, particularly those buildings in off-grid locations, but also those where there may be limited available capacity in the infrastructure of the national grid. In these situations, it isn't always feasible to decarbonise your heating system by installing a heat pump.  

And I think this is a good example of where we need to employ various heating technologies to meet our net zero carbon aims. Essentially, I think solid fuels are best used away from densely occupied areas such as towns and cities. Another time when this technology works well is when there is a local sustainable fuel source.  

One of the best examples that I've seen is a biomass installation installed near to an arboretum that can supply the fuel. The flip side of this though is when biomass plant in the UK has been fired using fuel imported from South America and Canada, and it's really concerned me when fuel described as being sustainable is shipped internationally over that kind of distance with all of the associated transportation emissions. It's just nonsense really.  

So there are a couple of times that I've been involved with solid fuels in my role at Historic England, and the first one that I've only just started being involved in recently is a large historical home. And this home has an existing biomass boiler which is shown in the photographs. Apologies, it's not very clear, but this boiler only heats a small proportion of the home, and they have got significant plans to replace the biomass boiler redesign the outside area, and install a modern heating system throughout their home. And they're looking at a new biomass plant, and I'm involved to provide technical advice about the best way to do this whilst also protecting the significant Grade I listed building.  

The photos don't do this place justice at all. It is an amazing place, but unfortunately I can't disclose the location of this one. I've talked with them about the fuel source and exploring the possibility of filtering the products of combustion to reduce the air pollution. This site has got already a local fuel supplier, and the prevailing wind appears to take the products of combustion away from the direction of the home. And it is a very rural location, so I don't think it is likely that they will actually install a filtration system.  

The other case study was in 2024 when a homeowner of a Grade II listed cottage located rural regularly was hoping that we could give them a dispensation to use coal in their fireplace. And their reasoning for the request was that the fireplace itself was part of the historic listing, which is quite common, and they claimed that they were no longer able to purchase coal and the smokeless alternatives were burning for too long and that they were burning too hot.  

I made several attempts to contact their fuel supplier, but they didn't engage. The outcome was that I couldn't see any reason to recommend a dispensation to burn coal. I'm not even sure if that is something that we could permit, but it wasn't something that I was comfortable to recommend.  

Now interestingly though, there is one area of England where you are still permitted to burn coal. However, it has to be locally mined coal. And Matt, I don't know if we can get that second poll up, because on that subject, I'd like to know where you think in England that you are still permitted to burn locally mined coal? And you've got 4 options there, and your choices are the Peak District, the Forest of Dean, the Lake District, or the New Forest.  

Now, I think this is a slightly unusual question and one that doesn't follow any real logic unless you know the answer already. And actually, looking at your responses, I can tell you that 48% of you, 58 of you, have got this right. It is actually the Forest of Dean. The next closest option was the Peak District, and I can understand that with various mining communities being around there. But well done to those 61 or so of you that voted for the Forest of Dean. And that's absolutely right.  

And yes, the Forest of Dean is the only place in England where you are permitted to burn locally mined coal. If you're not sure where that is, it's a rural area of Gloucestershire close to the Welsh border. And the reason for this permit is historical and linked to the free miners and a cultural heritage, right?  

And that leads me nicely into considering what improvements can be made. I would like to see more focus from everyone involved in solid fuel burning to reduce the health risk for users in the general public. I mentioned a filtration system in one of the case studies, and there are a couple of type of filters, but this type which I'm showing is an electrostatic type, which the manufacturer claims can reduce the number of particles by 95%.  

Now, I don't have any experience of this type of filter, so I can't recommend it. And also, I'm not sure if it would be permitted for installation in a significant historic building. But I did contact this particular manufacturer to understand more about how the particles are removed, and they provided a good clear response, actually. They— what they said was the way the system works is the charged particles are attracted to the mesh that is fitted in the filter And during startup, when the filter is activated by temperature, the fan gives a 2-second mechanical rattle which shakes the mesh and it knocks off any of the large collected particles which then drop back inside the flue to be re-burned. What we do know though is that the fuel choice, the type of solid burning appliance, and how we use and maintain the appliance can make a big improvement to the environmental and health considerations.  

So on the next few slides, I'm going to share a few resources that can be accessed, and you've got a choice here. You've got a very long website address that is on the screen, or if you've got a smartphone, on the next few slides you're going to see a few QR codes which will hopefully be easier for you to access if you're interested. And if you don't have a smartphone, then you can always take a photo of the very long web address.  

So in terms of Historic England resources on the subject of solid fuels, we've got this web page about open fires, chimneys and flues, and this covers a range of information including flue liners and ventilated caps. And then on our low and zero carbon web pages, there is a short section on biomass. I'll just give you a moment to capture anything that you want to there.  

And keeping with the theme of low carbon heating, I want to share how much work regarding heat pumps in older buildings that we've covered in other Technical Tuesday webinars. And all of these webinars are recorded and freely available. Our first one in 2022 covered how heat pumps work. Then we did a series of webinars in 2023 and '24 covering the viability of air, ground, and water source heat pumps. And this work included case studies that we could learn from.  

Last year did a webinar on all of the myths and misconceptions surrounding heat pumps. And then our most recent webinar in April last year covered the environmental impact of heat pumps and how they can be a sustainable heating option, even when you factor in the embodied carbon and the refrigerants used in this technology.  

And I thought it'd be worthwhile highlighting the publications which formed the content for some of those heat pump webinars. And this publication looked at the viability of air source heat pumps in historic buildings, and that one was published in 2023. And the QR codes on the next few slides take you to the download page where it's freely available.  

The next publication was published last September, and it investigates the viability of ground source heat pumps in historic buildings. Again, there's your QR code for the webpage. And a second air source heat pump investigation was published in January, and this one focused on 5 larger case studies. I'm going to stop mentioning those QR codes from now on.  

And finally, we've got this publication from January again that investigates the viability of water source heat pumps in historic buildings. Apologies if that was a lot of information, but I was really keen to share what we've been doing, and I'm really pleased with this series of heat pump investigations that I've worked on.  

And that's it for me on the subject of solid fuels. The QR code will take you to my LinkedIn account, so please feel free to connect or follow on there if you'd like to be kept up to date with our work. And we've got plenty of time for questions now, so if you haven't already asked anything yet, please do put your queries in the webinar chat. And a big thank you for listening. 

Matt Faber: Dan, thank you so much! Absolutely fascinating presentation. I have to say, on a personal note, using fuel oil and having a fire as well, I'm feeling a bit guilty right now. 

Dan McNaughton: It's not my intention at all, Matt. And actually, you could see from that, we could see for that first poll just how many people are using solid fuel appliances. Hence the warning. 

Matt Faber: We're not trying to preach. It's not going to go away anytime soon, I don't think, is it? 

Dan McNaughton: No. 

Matt Faber: Okay, let's move on to the Q&A. We have a few questions here for you. Fantastic! Can you see those questions? 

Dan McNaughton: Yeah, I'll have a quick read and pick one out. I mean, there's a few I don't know. Somebody's asked about Pete, and we've had a question. I'll just read it out actually. It says, where does Pete fit into this scale of badness? That's Pete the ground-covered oil, not Pete the person. He says, we're off to Skye this week and they have a stove and Pete store where we're going.  

Well, I'd actually say if you're off to Skye, just enjoy it, please. I'm really not trying to put you off anything. I think there are all sorts of environmental things with releasing various forms of carbon in the ground, whether that's melting Arctic tundra or burning peat. But I don't have any experience of it, so please enjoy your time away. It's a fantastic place there. I'm going to read out the very first question. It looks like a good one.  

So I've got a stove, a log burner, I've got to say, if anyone else has got any questions, please feel free to put your name in and then I'll know who's asking the question. But this one with the log burner, it says they only use it occasionally because it causes air pollution in the room and they're worried about breathing this smoky air in. It says, is there a simple but effective monitor one can buy to warn of the danger?  

Now I'm not into advertising or anything else, and I'm not sure if you'll be able to see it, probably not with the blurriness. It's not actually 50 pence. I put that on to make the kids think, make my children think that it's not valuable. But I have got an air quality sensor. Our team's actually bought a few of them in the past month or so because we've been looking at air quality when we've been, you know, looking at various wood burning appliances.  

And yes, it's quite enlightening understanding, what's going on. I won't recommend this particular one or do anything like that because I'm— for all sorts of reasons. But as a rough budget cost, I think it's around about £100, this sensor. But I do have some reservations about the accuracy. I think it's plus or minus 10%, so we've got to exercise a degree of caution with any results that we're seeing. But certainly we're seeing big spikes, not only with solid fuel burning appliances, but with things like cooking, everyday activities in the home.  

And if anyone's ever doing any DIY, one of our colleagues was talking about a big spike when they were soldering pipework recently. So I still think there's a lot to learn in terms of awareness of air quality. And I've got to say, indoor air quality and external is quite a passion of mine.  So I think you'll hear more on the subject. Hopefully that's helpful.  

So there's another question, and this one's quite topical, especially with the war that's going on at the moment and what's happening with fuel prices which is affecting many of us. So this question says, hi Dan, with the cost of energy ever increasing, many friends burn all types of wood. I think I've got a bit of that going on near where I live as well. And he has said, would you recommend this, or would you suggest that seasoned logs from a sustainable supplier are the best fuel for heat generation in the wood burner?  

So I think there's a couple of things in that, and I don't have a wood burner myself, so I can't pretend to be an expert on this subject. But if you remember the website, the government website that did talk about ready-to-burn fuel. And one of the things in that is the moisture content is much lower. And I haven't really explained to you today what— why scientifically, why the moisture content affects the burning. But it's essentially, if you've got moist fuel, you spend that extra bit of energy, that sort of hidden or latent energy, evaporating that moisture as part of the products of combustion.  

So that's why you get less useful heat, heat out of it. And so there's a little bit of an explanation. Yeah, there are reasons for it, but I'm also sympathetic to people's needs to keep warm as well. What you don't want to be doing is burning things which have got pressure treatments on them or paints and other nasties, because all of those pollution levels which I've shared today would go through the roof and wouldn't do you any good at all.  

Somebody's asked, doesn't biomass fuel have a large carbon footprint? I actually, if you look at because of that sequestration argument, the carbon footprint can be relatively low even when you're looking at transportation emissions. But I think I've hopefully explained that there's a bigger picture in terms of emissions.  

And yeah, some of the fuel supply issues I've seen with biomass are quite scary. You need to really understand where you're getting your fuel from and understand that supply chain to really understand the carbon emissions. There's a question about a guidance note on this subject. Does Historic England have one? They think it'd be really useful. No, I don't believe so.  

I mean, we've clearly got those web pages, which may be time to revisit and update actually with different things that we're learning. But I don't want to create more work for myself. But no, the whole point of today is to share what we do know and help improve people's knowledge and awareness without trying to tell people what to do, if that makes sense. I think that's about it for now, unless there's anything else, any more questions. We've certainly got time if you want to type a question in the next minute or so. I'll have a look at those. 

Matt: Whilst we're waiting for questions to come in, Dan, just a little personal experience on the subject. When I first moved to the house that I currently live in, which had an open fire, I didn't understand this topic in any shape or form. And yes, as you can imagine, I threw some rather questionable types of wood on that fire.  

And I do remember putting some tanalised wood on the fire which resulted in evacuation. Well, bright green sparks travelling at high velocity up my chimney. And given that I live in a thatched cottage, yes, seeing green sparks coming out of my chimney top was a little bit, yeah, a little bit anxiety-making. But I did speak to a local supplier of fuel wood.  

Yeah. And he mentioned to me that all— well, this is, this is quoting him— all wood sold for fire, for burning, has, has to be kiln dried but he said, but actually in the process that he has his own kiln, he dries his own wood but he said the problem there is I use as much wood in the kiln drying, creating the heat to dry the wood, that I'm actually supplying. Is that actually something that you've heard of? 

Dan McNaughton: No, no, I haven't. It does sound like quite a carbon-intensive…. 

Matt Faber: I raised an eyebrow when he said that, but…. 

Dan McNaughton: I'm sure it's… I can tell you something that I experienced recently. It was hotel I was staying in in Dartmoor a couple of weeks ago, and I went to meet some friends in the bar, and the open fire wasn't going in this room, but as I walked in, you could barely see my friends. It was so dense, the smoke. And I'm quite sensitive to sort of smells, pollutants, things like that, without all the electronic devices.  

And I walked in there, said, look, there's something wrong in here, walked out. And because my friends have been sat gradually over time in this room, they hadn't noticed it. But basically, because of wind pressure, we had this downdraft from what must be a really dirty chimney that essentially flooded the room with the smoke.  

I mean, I just grabbed my beverage and left them, went to a different area of the hotel, but they came out stinking. And I could— and they were all coughing the next day. So it's not just the fire burning process itself. It's other things when they're not maintained that can cause you problems. Did we get any more questions? 

Matt Faber: Yeah, in the chat, if you want to sort of backscroll, there's a few coming in there. 

Dan McNaughton: Okay, so Mary's said something. It might not relate directly to wood burning, but she said, I've been told I need to keep a gas boiler. I said, don't have space for larger radiators in Grade I1listed buildings. So what I recommend, Mary, that we— Matt… Matt, who's on the call with me, he's got a list of all of the website links which I've shared today and which we'll share to all of you. Have a look at the heat pump related webinars, if that's where this query is going, because there's different ways to work with your existing radiators in historic buildings.  

So sometimes you can keep what you've got, especially if they're nicer old column radiators or historic radiators, got historical significance in their own right, but, and supplement those radiators with additional radiators where required. And other times they will need replacing, but there isn't a hard and fast rule with that. And I think sometimes some installers will want to install giant triple panel radiators.  

Well, I know this is the fact, to avoid them having to do any calculations and assessing the existing heat emitters. So there isn't a hard and fast rule, but we do have lots of case studies and examples now of where heat pumps have been installed successfully, if that's where your question was going. Somebody has asked about other filtration systems available, other than the rather tall example you showed in the slides. That's from Simon.  

Yeah, that was my first impression of the filter I showed in the slides, that it was quite tall, it was shiny. I'm looking at a Grade I listed building, will it be approved? And that side of things, just from an aesthetic point of view. There is another type, but I don't know much about it. Yeah, it may be more expensive, but you can get a ceramic type of filter.  

So again, I think there's a bit more, everyone needs to learn about this technology. But it is interesting that you don't see these filters installed in many places. So let me just— I'm still just reading through a few things. Somebody's added to the peak query, actually. The very first one I read the person that's visiting Skye, unless it's the same person.  

So this person, Grant, went to Ireland to stay in a traditional thatched cottage, a bit like yourself, Matt, and they were only allowed to use peat on the fire because it gives off a low heat, so no problems with any sparks being a fire risk to the thatch roof. And you and I have talked about this, Matt, recently, haven't we? Insurance and thatched roofs and sparks. 

Matt Faber: That's a whole other webinar. 

Dan McNaughton: Yeah, yeah, it's definitely not my expertise, that one, but thank you for contributing that one. Oh, this is brilliant. Nigel recommended the use of a Gurney type of stove in a redundant church using an old flue. Is there such a thing available anymore? I don't think so, but I'm part of CIBSE Heritage and Retrofit, special interest group for our engineering institution, and we are quite impartial to a Gurney stove when we find them.  

And yeah, we try and protect those examples we've got left because they're fantastic. And you know what, at the time they did a particularly good, you know, they did a good job of heating different spaces. I think the problem you've got nowadays is, but I don't…. I don't think there is a modern equivalent. No, Nigel, but…. but no, it's an interesting point. And Trudy, who I know, has said there's something magical and empowering about cutting your own timber, storing it, and feeding the wood burner if used responsibly.  

And I think I've had a chat with Trudy before because I think she's got a wood burner where she works as well, her office, and it works really well for her. I'm definitely— I hope that message has come across loud and clear that I'm not trying to deter you from doing anything today, but do want to sort of make aware of different things. 

And I think I'm going to leave it there, Matt, if that's all right. If you want to wrap up, thank you!  

Big, big thank you from me to everyone for engaging well today!  

Really enjoyed that! And thank you! Special thanks to Matt as well, because this is a bit of a last-minute stand-in, wasn't it? So thank you, Matt, and thank you everyone!