At HVCA’s recent Open Homes Question time Professor Michael Corcoran mentioned that recent research had raised concerns that wood stoves might be bad for your health.
Jeremy Wight, HVCA Chair and a retired Director of Public Health, replied as follows.
Thank you very much for sending this link. It’s a very interesting paper, especially to a public health doctor (albeit retired) who loves his wood burning stove! Full disclosure, I am reading and writing this with my stove lit.
Let me say from the outset that I find it completely plausible that indoor air pollution as a result of having a woodburning stove increases the risk of lung cancer and quite probably other diseases (of which more anon). The crucial question is by how much. After all, there are lots of things we do that increase the risk of something bad happening, for example walking or cycling on a busy road, but we make a judgement that the increased risk is worth the benefits that accrue.
Clearly, it would be impossible to do a randomised controlled trial of woodburner use, not least because it would need to be run for I guess at least 10 years. Hitherto most evidence has come from case control studies, which are inherently weak. This is the first cohort study I have seen on the subject, and as such, is as good as it is likely to get in terms of evidence.
But the key thing to consider (and forgive me if this is all well known to you) is not the increase in relative risk (‘people who use woodburners are 70% more likely to get cancer than those who don’t’), but rather the increase in absolute risk (the risk of lung cancer in people who use woodburners is increased from 0.65% over ten years to 0.95%). So over a ten year period, approximately 0.3%, additional people will get lung cancer. Or to put it another way, if 333 people use a woodburner for ten years, one of them will get lung cancer who would not otherwise have done so. This is the key piece of information that should be shared with woodburner users (or those considering it).
Three other complicating factors worth considering:
The study did not differentiate between open fires and stoves, nor between different types of stoves. Doubtless a modern well maintained stove causes less indoor air pollution than older models, and both, less than an open fire. The risk with a new stove, burning only very dry wood, may therefore be presumed to be significantly less than identified here.
But it did not look at the increased risk of other diseases. This is likely. For example, cigarette smoking causes more deaths through the increased risk of heart disease, than the increased risk of cancer. It would be surprising if indoor air pollution from woodburners did not cause an increase in cardiac disease. (There is also reference to an increased risk of breast cancer, which I find interesting, because as far as I know, tobacco smoking has not been shown to increase breast cancer risk.)
And what’s more.. there is clearly a dose response effect, and the highest category of exposure in the study was >30 days per year. People like me who use our stoves much more than 30 days per year will be at higher risk than those who only use them for 30 days… And what’s more, I’ve been using one for more than 10 years!
This hasn’t yet persuaded me to stop using mine! My judgement is that the benefits I accrue – warmth, a feeling of cosiness that is independent of temperature – are worth an increased risk that may be of the order of 0.3% over ten years (with a wide range of uncertainty). But putting my public health hat back on again, the thing I am more concerned about with wood burners is the outdoor air pollution they cause, not least because while I can choose how much indoor air pollution I want to expose myself to, what I vent into the atmosphere is inflicted on everyone out there, without them having any say in the matter. This is why I think there is a strong case for woodburners being prohibited in cities.
And of course wood burning is a source of CO2 emissions, but that is another argument.
If you are worried about particulates from you stove or have a child or elderly relative who might be vulnerable you might consider installing a HEPA (high-efficiency particulate absorbing) filter. They are portable and fairly cheap. John de Carteret reports that his filter reacts immediately shoots into the red whenever he opens the stove door to add wood. On the other hand, hominids and humans have been sitting around fires for a least 400,000 years. (https://royalsocietypublishing.org/doi/10.1098/rstb.2015.0164).
Two other points worth mentioning –
The research drawing attention to the health risk of particulates doesn’t distinguish between types of particulate matter. it may be that wood smoke is less harmful than other sources of particulates.
In terms of reducing our carbon emissions, wood stoves only make sense if we have a local source of sustainable timer, for example from our own woodland or from a local tree surgeon, and the amount of timber being burnt is being replaced by natural growth.