“The most damaging and dirtiest heating method” – an expert explains how wood-burning stoves are now polluting entire residential areas

Make a fire in the evening. Sit comfortably in front of the fireplace. Let the flames warm you. This is super relaxing and can only be healthy. Wrong, says Achim Dittler, professor at the Karlsruhe Institute of Technology (KIT).

In an interview with FOCUS online, the scientist explains why the level of pollution in residential areas is currently higher than on main roads in large cities, why the smoke gases released can be extremely harmful to health and why it is best to avoid burning wood.

FOCUS online: When I step outside the door in the evening, I immediately have this pungent, rather penetrating smell in my nose. Am I imagining it?

Achim Dittler: No, you are not imagining it. They describe what many people are currently experiencing, especially in the evening and night hours. This acrid smell often reeks of forest fires or campfires. It is therefore clear – and you can also see this from the chimneys – that wood stoves are the cause behind the smell.

Some days it’s worse than others. Why is that?

Dittler: Either to the weather conditions or that more people heat with wood. However, a stove is often enough to smoke an area between 100 and 200 meters in such a way that it can become more than a nuisance for people.

Particulate matter promotes diabetes and dementia

Which pollutants are released here?

Dittler: Carbon monoxide, nitrogen oxides, unburned hydrocarbons and a whole range of other pollutants that can also be found in cigarette smoke. In addition, carcinogenic soot and ash are emitted as fine dust particles. Basically, it’s like passive smoking.

So this wood smoke is harmful to your health?

Dittler: We have examined the topic in detail in a study in Stutensee in the district of Karlsruhe. In the simplest case, it is “only” an odor nuisance and you cannot ventilate your living space. Ultimately, this limits your quality of life. However, if you have a mechanical ventilation system in your living space and outside air is continuously drawn in, then your living space will be filled with diluted smoke. In extreme cases, those affected report acute symptoms of mild smoke inhalation, i.e. headaches, nausea and irritation of the mucous membranes. In 2019, we reported on the long-term consequences of increased exposure to particulate matter in the Leopoldina statement “Clean Air”. In addition to lung diseases, connections with cardiovascular diseases, the development of type 2 diabetes and a faster development of dementia are mentioned there.

Still, people are burning wood like there’s no tomorrow. What are the reasons?

Dittler: People are looking for a cheaper alternative to oil and gas. That means you want to save. There is also the fear that there may not be enough gas for heating. And, of course, cosiness and homeliness are also associated with a wood-burning stove. But one thing is certain: Heating with wood is the most climate-damaging and dirtiest heating method there is. Saving gas is therefore at the expense of the quality of the air we breathe in residential areas.

#holzofengate and what the authorities are doing against fine dust

What is #holzofengate all about?

Dittler: You know Dieselgate. The trigger was that the real emission values ​​for nitrogen oxides were higher than on the test bench. At Holzofengate it is equivalent. These single-room furnaces only meet the acceptance conditions under laboratory conditions in certain operating modes. In reality, these stoves emit more pollutants than on the test bench, also because the fuel quality is not regulated, the filling quantity is often not clear and the combustion air supply is not regulated – and often in densely populated residential areas for many hours. What then affects the individual as an immission is many times higher than on main roads in large cities. We measured this and had an hourly average pollution level of the breathing air with respirable fine dust in residential areas that was three times higher than on one of the most heavily polluted main roads in Germany.

Diesel cars are gradually being banned from German inner cities. What are the authorities doing about the wood stoves?

Dittler: Nothing.

Where are the limits?

Dittler: That’s exactly the point. Wood stove gate is a problem of regulation. The emission limits of the ovens are far too lax. These are many times higher than in a car. In addition, the immission – i.e. the air quality – is really neglected in Germany. In the case of respirable particulate matter (PM 2.5), there is only an annual mean value of 25 micrograms per cubic meter. In winter, however, peak values ​​of over 100 micrograms per cubic meter are measured in some places in the evening. Of course, these are lost in the annual average.

This means?

An annual mean value is unsuitable for recognizing and eliminating passive smoking in the evening during the heating period. That’s why the authorities aren’t doing anything. If a PM2.5 daily average were to be introduced, as the WHO is now proposing at 15 micrograms per cubic meter, many cities would have a problem. In Stutensee near Karlsruhe alone, the daily average of 15 micrograms per cubic meter was exceeded three times last week.

Are wood stoves really worse than cars?

Dittler: Of course. Cars have highly effective exhaust gas cleaning systems, especially with closed particle filters, which hold back soot and ash very effectively. In the case of wood-burning stoves, much higher pollutant emissions are released into the breathing air in residential areas for many evening hours without exhaust gas cleaning.

“Wood stoves are sustainable and climate-neutral – a huge lie!”

Why does the wood stove still have such a good image?

Dittler: Because for decades it has been possible to market wood-burning stoves as sustainable, cosy, CO2 and climate-neutral. A big lie! People urgently need a knowledge update here, to quote health researcher Hans Rosling.

There is hardly a new building without a fireplace or Swedish stove.

Dittler: In the quantity in which the stoves have now been installed, this has an impact: on the quality of the air we breathe, but also on the need for firewood and thus on the forests. The German forest is becoming less and less of a net CO2 sink. The people who built something like this were deceived.

How did that happen?

Dittler: Thanks to clever marketing, wood stove owners mistakenly think they are doing something good for the climate and environment and are particularly sustainable. A rethink is required here. Heating with wood is by no means climate-neutral. Of course, it’s difficult to admit that to yourself when the stove was only installed two years ago. This is a huge hurdle and is also related to admitting one’s own mistake.

“Outdated knowledge for many people”

You get some angry replies.

Dittler: The headwind comes from the fact that many people have an outdated level of knowledge that is deeply rooted. Revising a preconceived notion is of course not easy. Much more often I get positive encouragement for our educational work. Many of those affected turn to us for help. Unfortunately we can’t really help.

What can you do?

Dittler: You have to explain. About the fact that burning wood emits far more pollutants and CO2 than any gas or oil heating system. About letting the forest grow instead of burning it. If you are toying with the idea of ​​buying such an oven, I recommend that you don’t. Look for alternatives.

And the politics?

Dittler: They need to take this topic more seriously. Basically, you should get out of the wood combustion and end the funding. In terms of CO2 and pollutant emissions, wood is not an alternative to oil or gas. If one does not want to ban wood firing, the emission values ​​for the systems should at least be tightened so that citizens in their living environment do not have to experience any nuisance or health hazards in their living environment. For many people, the quality of life in their own four walls and in the immediate vicinity is no longer given. Operating bans should also be possible in the event of a specific risk. When planning a new development area, municipalities could specify, for example, that no solid fuel heating systems are permitted in this area. This is doing people a great favor when it comes to the air they breathe.

If you’re invited and there’s a fire burning in the hearth – say what?

Dittler: Of course I’ll say something, even if it’s not exactly the burner at the moment. A lot of people I know have already changed their minds anyway and are skipping the stove. You can achieve a lot of positive things on a small scale with education.

Do you have a wood stove at home?

Dittler: A wood stove was already in there when we moved in. I’m not tearing it out, but I’m not running it either.

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