Wood Burning Stoves in the popular science press

[SteamyTea]

About time this started to go mainstream.
https://www.newscientist.com/article/2119595-wood-burners-london-air-pollution-is-just-tip-of-the-iceberg/

By Michael Le Page

Last week, air pollution in London soared to heights not seen since 2011. The usual suspects were named and shamed, including traffic fumes and a lack of wind. But joining them was a surprising culprit.

“We think about half of the peak was from wood smoke,” says Timothy Baker, part of a team at King’s College London that monitors air pollution.

The trendy log-burning stoves producing much of this pollution are marketed as a source of renewable energy that can cut fuel bills while helping reduce global warming. But recent findings suggest they pose a serious threat to the health of their owners, and are also accelerating climate change in the short term.

If nothing is done to discourage log burning in homes, it could become the biggest source of air pollution in cities like London. In the UK as a whole, wood burning is already officially the single biggest source of an especially nasty form of air pollution.

“I love sitting by a log fire as much as the next person but maybe we need to think again before it’s too late,” says climate scientist Piers Forster of the University of Leeds, UK.

Air pollution is awful for our health. The smallest particles get into our blood and even our brains, increasing the risk of many disorders including heart disease.
Natural killer

Children are especially vulnerable: high pollution levels impair their lung and brain development. Air pollution from all sources is estimated to cause some 10,000 premature deaths a year in London alone, where it frequently exceeds legal limits.

Wood smoke may be natural, but it contains many of the same harmful substances as cigarette smoke. It’s a massive killer worldwide, causing as many as 4 million premature deaths every year through indoor air pollution.

In the UK, however, the problem with pollution from wood fires was thought to have been solved by clean air laws introduced in the 1950s, which banned wood burning in open fires in cities. “The official view is that residential wood burning is a thing of the past,” says Gary Fuller of King’s College London.

Yet logs can still be burned in officially approved stoves in cities. Sales of these stoves have soared in the past decade, rising to nearly 200,000 a year. They are marketed as a way for people to drastically reduce their carbon emissions and save on fuel costs.

Even modern stoves described as “low emission” are highly polluting. And in an echo of the diesel car emissions scandal, measurements during actual use in homes show that the stoves produce more pollution than lab tests suggest.

In the “smokeless” fumes coming from the chimney of a house with a modern “eco-friendly” wood burner, Kåre Press-Kristensen of the Danish Ecological Council has measured 500,000 microscopic particles per cubic centimetre. The same equipment finds fewer than 1000 particles per cm3 in the exhaust fumes of a modern truck. The wood stove was certified as meeting Nordic Swan Ecolabel emission standards, which are stricter than the ones stoves in the UK have to meet.
Big in London

What this means is that a small increase in wood-burning stoves can produce a big increase in pollution. In Copenhagen, a city of 600,000 people, just 16,000 wood stoves produce more PM2.5 pollution – the most dangerous particles, smaller than 2.5 micrometres – during winter than traffic does all year round, says Press-Kristensen.

Wood burning is becoming a big problem in London, too. In 2010, when Fuller analysed particulate pollution to discover its source, he found that 10 per cent of all the city’s wintertime pollution was from wood.

There are many reasons to think that figure is higher now. A 2015 government survey found that domestic wood consumption in the UK was three higher than previous estimates, with 7 per cent of respondents reporting that they burned logs. “Wood consumption is increasing substantially,” says Eddy Mitchell at the University of Leeds, UK.

When he, Forster and others fed the data on wood consumption into a computer model of air pollution, their conclusion was disturbing: PM2.5 pollution from residential stoves is soaring in the UK (see diagram, below).

“There is a real risk that if we have a lot more residential wood burning then it could undo our other efforts to control air pollution,” says Fuller.

The harm far exceeds traffic pollution, he says. While people are exposed to high levels of traffic pollution mainly when travelling on busy streets, wood burning produces huge amounts of pollution where people live, when they are at home.
Indoor smog

Press-Kristensen has been measuring that pollution inside homes in Copenhagen. In three out of seven tests done so far, he has found very high levels. In one home with a modern log-burning stove, he found particulate levels several times higher than the highest ever recorded outdoors there (see diagram, above).

So do the health impacts outweigh any climate benefits? Astonishingly, there might not be any climate benefits, at least in the short term.

Burning logs is often touted as being carbon-neutral. The idea is that trees soak up as much carbon dioxide when growing as they release when burned.

In fact, numerous studies show that wood burning is not carbon-neutral, and can sometimes be worse than burning coal. There are emissions from transport and processing. Logs are often pre-dried in kilns, for instance.

Burning wood also emits black carbon – soot – that warms the atmosphere during the short time it remains in the air. Most studies ignore this, but Mitchell and Forster calculate that over 20 years – the timescale that matters if we don’t want the world to go too far above 2°C of warming – soot cancels out half the carbon benefits of all wood burning.

For home wood burning, the figures are even worse. “On a 20-year timescale, wood stoves provide little or no benefit, but they do on the 100-year timescale as they remove some of the long-term warming effect of CO2 emissions,” says Forster.

Press-Kristensen’s calculations show much the same thing. And both sets of findings almost certainly underestimate the problem, because they assume wood burning is carbon-neutral.

Defenders of wood stoves point out that there is a lot of uncertainty about how much black carbon is emitted when wood is burned and how large its effect is. Patricia Thornley of the University of Manchester, UK, thinks we need more real-world measurements before coming to conclusions.

But the uncertainties cut both ways. For instance, the effects of black carbon can be amplified if it is deposited on snow and melts it, exposing dark land that absorbs more heat. It’s possible soot from wood burning is contributing to the fall in spring snow cover in Europe, but it’s very hard to study.

More research is needed to pin down the precise climatic effects of wood burning, which can vary hugely depending on factors such as the source of wood and where the pollution goes. What is clear, however, is that burning logs in homes in towns and cities is not the best use of the wood we have.

It produces more pollution than wood-burning power plants that can be fitted with expensive filters, it produces that harmful pollution where lots of people live, and it has the least climate benefits, if any. “If we are going to burn biomass to meet climate targets, then we ought to do it in big, remote power stations,” says Martin Williams of King’s College London, who is studying the health impacts of the ways the UK could meet its climate targets.

Most researchers say it isn’t their role to make policy recommendations, but it would be best if cities like London discourage private wood burning before it becomes an even bigger health problem. At the moment, all the focus is on diesel vehicles.

Press-Kristensen doubts governments will ban wood-burning; France recently backtracked on a proposed ban on open fires, for example. Instead, he proposes installing heat sensors in chimneys and taxing people when they burn wood, with the level of tax depending on how polluting the appliance is.

Most importantly, governments must not ignore health impacts when deciding climate policies, says Press-Kristensen. “I like fires, but I have to say they are as polluting as hell,” he says.

 

Thinking of getting a wood-burner?

Wood-burning stoves are touted as an eco-friendly way to heat your house cheaply. But tests now show that even new, properly installed stoves can produce dangerous levels of outdoor and indoor pollution (see main story). What other options are there?

Consider instead

Stick with gas or oil for heating, and spend your money on insulation. Get a heat pump if you can afford it

Fake it

You can get the same cosy feeling from a log-effect electric or gas fireplace, the best of which are hard to distinguish from the real thing

Already have a wood-burner?

Here’s how to minimise its effects:

Don't burn scrap wood

Scrap wood or painted wood can release highly toxic substances such as arsenic when burned

Burn wood that's just right

Burning dry wood with a moisture content of about 20 per cent minimises pollution. But if wood is wetter or drier than that, pollution increases

 

[Ferdinand]

I can't yet discern how much of this story is hyperbole and marketing by attention-seeking grant-seeking academics.

 

The last one a few days ago was "London is more polluted than Beijing" as the tabloid interviewer on R4 Today was yelling at the politician, where as I understood the London reading to be a single point peak reading, and the Beijing one to be more of a background average (ie Mr Today was spouting b*ll*cks as per umpteen times per morning).

 

I argued that here:

http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14864&page=1#Item_4

 

If the harm is "far greater than from traffic pollution" then why do we have a huge flap about diesels at the moment?

 

And did he actually just imply a sample size of one?

 

Can you clarify, ST?

 

Cheers

 

Ferdinand

Edited February 2, 2017 by Ferdinand

[daiking]

I only realised this was an issue after seeing it was a (very) contentious issue on ebuild.

 

We (my wife and I) did want a stove in our house in a built up area, you know the whole lifestyle thing - we'd just cut down several large trees so had plenty of wood*. What put us off was not the environmental issue but the frightening cost £3k+ even if we put it in an existing fireplace. Instead we got a whole gas fire package supplied and fitted for £1k and I doubt we use £50 of gas a year.

 

We would have been insane to install a stove.

 

*Sold the wood to some muppet for £100 after it had sat in my garden for 6 months.

[SteamyTea]

48 minutes ago, Ferdinand said:

Can you clarify, ST?

Not quickly, but with some research I possibly could. Just reread your question and worked out what you mean, the answer is 'it all depends on what you want to show, see my average car price

I think there are several issues getting mixed up.  This is not an argument about either cars or stoves, or smoking or not smoking.  Particulate air pollution is a cumulative issue, bit like lead poisoning, so reduction from any source is a good thing.

 

Academics, and the wood burning industries, should be chasing funding, that is how science works.  If you think the scientific process is all wrong, then that is a different issue and one unrelated to the data collected.

 

41 minutes ago, daiking said:

We would have been insane to install a stove.

Especially when you see the 'indoor' figures.  They confirm a calculation that @JSHarris did a while back, about the same as 50 diesel vehicles pumping the particulates into a living room.

Edited February 2, 2017 by SteamyTea

[ProDave]

It says what I have said for a long time, that a WBS is NOT carbon neutral and is not the answer to climate change.  Selling WBS's and boimass boilers on some phoney eco credential is verging on fraud.

 

I still like a stove and in a sparsely populated area like this and with ample free wood available I still think they are good, but in a town or city, or even a large village, and especially if you have to buy in your wood, then I think they are a bad idea. (I can't imagine many Londoners finding enough free wood lying around for the taking)
 

[Crofter]

You have to be careful about what your starting assumptions are. The article seems to be from the point of view that everybody should be on gas heating and the trend for stoves is simply a lifestyle choice.

 

However my experience is that there are still far too many people burning peat and coal on open fires. This is probably a geographical thing. The inefficiency of an open fire horrifies me and IMHO they should be banned. So I find it hard to get aboard the 'anti stove' bandwagon.

[SteamyTea]

16 minutes ago, Crofter said:

The article seems to be from the point of view that everybody should be on gas heating

In the UK most people are, and there is always LPG.

Then there is electricity.  Not many houses are without it.

It is easy to find an exception to most things, and very easy to do nothing because of that exception.  But that isn't the point of legislation.

 

22 minutes ago, ProDave said:

I still like a stove and in a sparsely populated area like this and with ample free wood available I still think they are good

Even when it can unknowingly greatly affect the health of the only person that is using it?  On that argument it is OK to dump any pollutant in a 'sparsely populated area'.

Edited February 2, 2017 by SteamyTea

[Jeremy Harris]

1 hour ago, SteamyTea said:

Especially when you see the 'indoor' figures.  They confirm a calculation that @JSHarris did a while back, about the same as 50 diesel vehicles pumping the particulates into a living room.

 

Indeed, they do.  I started looking into this around 10 or more years ago, after we'd been living in our old house (in a small and rural Wiltshire village) for about 5 years or so and had experienced several "smog events", where the valley filled up with a mix of fog and woodsmoke on cold, still days.

 

These "smog events" still happen; we had one a few weeks ago, and there's not a thing you can do to stop the pollution getting into your house.  Luckily, neither of us has had any noticeable health effects from this, but the elderly lady over the road was taken to hospital the morning after the last event, and when I saw her the other day she told me that the cause was the smog in the valley.  The funny thing is that she was one of those burning wood until around 8 or 9 years ago.  She stopped, and had a gas boiler fitted, only because the price of wood here was so high.  She's now a bit like a reformed smoker in terms of going around the village telling people of the evils of wood burning.

 

Apparently, the same "smog events" used to occur in the village we're moving to, but the PC and a group of residents got pretty active about stopping them, just by repeatedly pointing out the harm they cause.  They got bonfires stopped too, because, apparently, every time someone living low in the valley lit one on a still day a similar thing would happen, and the valley would fill with smoke.

Edited February 2, 2017 by JSHarris
typo, "the" when I meant "they"

[Crofter]

One odd thing I noticed in the article is that they claim that wood that is too dry (below 20% MC) causes more pollution. I'm not saying this is wrong, but I would very much like to understand the mechanism involved.

 

Also, there is room for education on correct use of stoves- I know people who insist on sitting with the stove door open, people who try to burn green wood ("it's OK if you use some coal too!") and, most commonly, people trying to keep their stove smouldering away at a low heat overnight. An extremely messy and polluting way to avoid having to relight it the next day.

[Jeremy Harris]

There are many pollutant sources from burning wood, and to a large extent what you get depends on the temperature of combustion and the moisture content.  The first is the toxic gases, which tend to be worse with damp wood, where a host of chemical reactions take place, together with the moisture, to release a wide range of compounds, some of which are carcinogenic, some of which are just toxic and some of which are reasonably harmless.  The second pollutant, and in my view the most insidious, as it's not readily observed, are the very fine particulates.  These tend to be more significant when burning very dry wood, just because often the particle size will be smaller.

 

In health terms, the visible smoke is a nuisance, and may make you cough a bit, but because of our reaction to smoke we tend to try and avoid it, plus it is mainly pretty large particles (which is why we can see it) and they tend not to penetrate well into closed areas.  It's the "invisible smoke"  that mainly presents the risk of smaller particulates being spread around, and we now know that these are potentially far more harmful than we first thought - it's why things like diesel vehicles now have particulate traps, and why power stations have something very similar.

 

These very tiny particulates can carry toxins across the lung tissue barrier and into our blood, and from there directly into all our organs, which is the reason there is so much concern about them.

 

 

[Crofter]

I wonder to what extent the stainless mesh fitted to my stove will alleviate particulate pollution- it is described as a soot catcher and is designed to burn off small airborne particles. One of the reasons my stove is rated at 89% efficiency, compared to less than 80% for most good stoves.

 

Another consider that comes to mind, that might explain people's reluctance to accept the arguments against stoves, is that burning wood is as old as Homo Sapiens itself. Is there something about the higher temperatures reached in stoves that makes their emissions worse than what we have endured for the preceding millenia? Or is it just that for the last fifty years or so we have had cleaner alternatives?

[Jeremy Harris]

The mesh won't make any difference to the harmful particulates, as they are incredibly tiny - tiny enough to pass into your bloodstream through your lungs, and beyond.

 

The reason we have health concerns when our ancestors used fire apparently without harm, are many and varied.  Firstly, we live a great deal longer, so the effect of exposure to toxins is greater.  There are a large number of conditions that are inherited (and I carry genes for one of them) where the condition only manifests itself after prime reproductive age.  These evolved because we didn't need to evolve to combat them - few people lived beyond the age of 40 or so, even into the Middle Ages.  We are also now living in larger conurbations, at a much greater population density, and we live in smaller family units.  Whereas our ancient ancestors may have had one fire for a whole tribe or settlement, we have many thousands of them in towns and cities.

 

Temperature does have a big effect on the type of emissions, but burning hotter isn't always better.  It resolves some of the toxic compound problems that cool burning, in the presence of moisture, create (things like creosote, for example) but it can increase the emissions of NOx and smaller particulates.  

 

The main issue is that wood stoves have become popular in settlements, and frankly that's where the higher risks are.  If you live in open countryside, then at least it's only yourself and your own family that are likely to be exposed, not dozens of people around you.  I've mentioned it before, but our village fills with smoke on cold, still, days from just three houses, out of around 400, that persist in burning wood.

 

If those houses were not in the bottom of a valley, very close to many other houses, then their wood burning would largely be just their problem, and frankly I'm of the view that people should have the freedom to do as they wish, as long as it doesn't cause potential harm to others.  I view things like smoking, drinking, etc in the same way - as long as people who indulge don't put me at risk then they should be allowed to do as they wish.

[SteamyTea]

2 hours ago, JSHarris said:

I view things like smoking, drinking, etc in the same way - as long as people who indulge don't put me at risk then they should be allowed to do as they wish.

But should they make a financial contribution to society, smokers, drinkers and drivers all do.

[joe90]

2 hours ago, JSHarris said:

 

The main issue is that wood stoves have become popular in settlements, and frankly that's where the higher risks are.  If you live in open countryside, then at least it's only yourself and your own family that are likely to be exposed, not dozens of people around you.  I've mentioned it before, but our village fills with smoke on cold, still, days from just three houses, out of around 400, that persist in burning wood.

 

This is the issue I argued over on the other place, building regs say the devise must not cause nuisance however it's built or used and I believe the authorities should have powers ( that they are not afraid of using) to condemn the use of any devise that causes nuisance. The argument over there is more about the devise being built to regs.

 

the analogy I like is that most legal cars can do 100 mph but if you break the speed limit you are causing nuisance and can and should be prosecuted for it.

[Jeremy Harris]

The issue of HETAS regs is a red herring, as it makes no reference at all to the actual emissions from any device, all it does is stipulate an installation method, and show that, under carefully controlled test conditions, a HETAS approved device will conform to some very, very lax regulations.

 

Smoke nuisance is an entirely separate thing, and nothing to do with stove installation, approval or anything else.  If the very best stove in the world is located where it causes a nuisance then it's in the wrong place and should not be used, irrespective of the approvals it has.  It's no different to anything else in that respect.  Say I buy a fully approved portable generator, then run it so it causes a noise or pollution problem - just because the thing's approved doesn't stop it being capable of causing a nuisance if it's run in the wrong place or at the wrong time.

 

Our PC have been trying to get our local EHO to investigate our air quality problems, but frankly the EHO just wants to dodge the issue, rather than properly investigate.  I strongly suspect he has a wood burning stove himself, he's that apathetic about addressing the pretty bad pollution problems we have from time to time.  Last I heard the PC were looking at whether to buy/hire some air quality monitoring kit, but apparently they've hit a road block with the EHO, in that he will only accept 14 days of continuous monitoring, no more, no less, and it may well be that the monitoring set up could miss a bad pollution event, because whenever there's a bit of wind about the problem literally gets blown away. 

 

Edited February 3, 2017 by JSHarris

[joe90]

Jeremy, I completely agree with you. Lax policy, lax officials with no will or teeth.

[SteamyTea]

What is the 14 consecutive days that the EHO is saying about.  Is it a real thing, or just something that they like to work to?

It should be possible to send in data from when there is a problem, not when there isn't surely.

Edited February 3, 2017 by SteamyTea

[Jeremy Harris]

1 hour ago, SteamyTea said:

What is the 14 consecutive days that the EHO is saying about.  Is it a real thing, or just something that they like to work to?

It should be possible to send in data from when there is a problem, not when there isn't surely.

 

TBH, I don't know.  As we're moving I'm staying out of it!

 

All I know is that the EHO has requested 14 days of continuous monitoring by an approved air quality sampling system, located in a fixed position through the 14 day period, and will only act if the air pollution level recorded exceeds a particular figure (not even sure what that is).  This is contrary to the complaint, which is that the smoke emissions interfere with the right of residents to enjoy their homes, and constitutes a nuisance, and should be dealt with by him on that basis.

[Gimp]

I was considering a wood burning stove for the build I've got planned in Wales, its on a hillside at the back of the village. However there are residential builds not far to either side slightly further up the hill. I know at least one of the nearby houses has a wood burning stove as smelt it while I was there (they kind of stink real bad particularly with damp wood) and the guy had a store of wood outside with a shelter that probably didn't protect the wood enough from the rain. Anyway, I'm not sure I would want to add to the problem and with the wind blowing it back to the neighbours or settling down in the valley it won't make me very popular with the neighbours I'm thinking. 

 

There is the advantage that there is a lot of common land that consists of a wooded hillside going up quite some way behind my site, so picking up wood would be free but its questionable if this would be in sufficient size or quantity without a real trek. Then I would have to cut it and while I would have sufficient totally dry storage in my proposed build I can't really see myself as being bothered long term to keep trekking up a hillside looking for wood, then having to keep chucking it in the stove, any clean out, maintenance, replacement, etc. I really don't see it as something I would want to do with the weather you get in Wales to go collecting wood, particularly when its rainy, cold, windy, etc. It might just get a pain in the bum to keep doing, I wouldn't know for sure until in that position but then it would be too late. I certainly wouldn't pay for wood it kind of defeats the object of a WBS for me I think. So I'll probably look at either gas or electric as some of them are quite nice these days. 

[SteamyTea]

One of the things that the report highlighted is that it is not just a problem for neighbours (or from neighbours).  Even using an approved stove the pollutants may be staying in your own house.

 

" Press-Kristensen has been measuring that pollution inside homes in Copenhagen. In three out of seven tests done so far, he has found very high levels. In one home with a modern log-burning stove, he found particulate levels several times higher than the highest ever recorded outdoors there (see diagram, above). "

 

And why would people collect timber when the weather is wet and cold.  Surely the idea is to get it when the weather is warm and dry and dry/store it until it is needed.

Edited February 8, 2017 by SteamyTea

[Crofter]

Wood burners are like fish... if it smells, something's not right.

[SteamyTea]

And when it don't smell, it ain't right either (I am allergic to fish).

[PeterW]

2 hours ago, SteamyTea said:

And why would people collect timber when the weather is wet and cold.  Surely the idea is to get it when the weather is warm and dry and dry/store it until it is needed.

Edited 2 hours ago by SteamyTea

 

So there are two types of "dry" wood, and that's the issue ..! I can put a log in a warm room for 72 hours and the outside moisture content can be as low as 10% - inside it will be 35-40% but most people don't know how to measure properly the moisture content of logs. 

 

The second log can be 10% in the middle but dunk in a bucket of water for 2 hours and it's 40% on the outside - this is a dry log stored badly ..! 

 

The biggest issue  is we have forgotten how to make fires and store wood - I would hazard a guess that anyone who cuts, splits and dries their own wood knows the right way whilst anyone who has a lifestyle stove and buys their overpriced "kiln dried" timber in neatly packaged pallets wouldn't know a dry log if it smacked them

across the back of the head ...! 

[Jeremy Harris]

32 minutes ago, PeterW said:

 

So there are two types of "dry" wood, and that's the issue ..! I can put a log in a warm room for 72 hours and the outside moisture content can be as low as 10% - inside it will be 35-40% but most people don't know how to measure properly the moisture content of logs. 

 

The second log can be 10% in the middle but dunk in a bucket of water for 2 hours and it's 40% on the outside - this is a dry log stored badly ..! 

 

The biggest issue  is we have forgotten how to make fires and store wood - I would hazard a guess that anyone who cuts, splits and dries their own wood knows the right way whilst anyone who has a lifestyle stove and buys their overpriced "kiln dried" timber in neatly packaged pallets wouldn't know a dry log if it smacked them

across the back of the head ...! 

 

 

I'm sure you're right.  My brother's winter business (during the summer he's a landscape gardener) is tree felling and supplying logs.  He has a Dutch barn, with slatted sides and a floor made up of pallets stacked two deep, and keeps all his cut and split firewood stacked in there for a couple of years, so he can get the moisture content down as low as is practicable.  He does this, funnily enough, because we had a wood burner around 25+ years ago, just when he was starting his business (under Thatcher's scheme to pay people £20 a week to start their own small business) and I was complaining about the problem of getting decently seasoned firewood.  The barn was going spare on Mother's farm, he ran his business from the farm (still does) and so he adapted it for drying firewood.  I'm pretty sure his long-standing repeat customers use him because he supplies dry firewood.

Edited February 8, 2017 by JSHarris

[SteamyTea]

The real problem is that even if the logs/pellets/chippings are at the correct moisture, the stove fitted correctly and used right, they still pollute like hell.

I think that message is not getting across.