As I write this the UK is in the biggest energy crisis of a generation. One serious consideration for many is a wood burning stove. They’re relatively cheap and many people have an abundant free fuel supply. But what about the emissions? THINK OF THE CHILDREN!! OK, I went down the rabbit hole…
This article is a bit of an evolutionary work in progress. I’ll add to it over time as I take more measurements at home and learn more from our wonderful viewers.
The shameful state of the UK energy industry
In the last 18 months our energy bills have risen from £105 to £351 per month, and we’re in a well insulated, small house. Gas prices have gone from 2.2p to around 10.2p / kWh. That’s a 436% increase. Electricity prices have also surged, from around 15p to 38.5p / kWh, a 256% increase. So I’m very pleased we installed a wood burning stove last year. It certainly takes the edge off but what’s all this I hear about emissions? Aren’t we trying to reduce levels of carbon dioxide in the atmosphere? And what about particulates?
Are wood burners really carbon neutral?
Yes, wood is generally regarded as a renewable fuel resource. Not as environmentally friendly as wind, solar or nuclear. But way better than coal or gas.
When trees grow they suck up CO2 from the atmosphere and release oxygen (O2). The carbon is stored in the wood until it’s burned when the process of combustion releases the CO2 back in to the air. So providing the trees are replenished (plant new ones… and some extra ones!) there is no net increase of carbon emissions. The carbon simply went from the air, to the tree and back to the air.
Trees don’t last forever so even if they’re not burned, they will still release the CO2. This happens naturally when they die and rot away. So we might as well make use of that free energy.
This is different from coal or gas where the carbon is locked up in the fuel source forever. By burning it we add extra carbon to the atmosphere that wasn’t there before. That’s a problem.
In our particular scenario we had a VERY overgrown garden. There were lots of dead trees and lots of trees that needed some severe pruning. As such we have an abundant supply of wood, all happily air drying in our log store. We air-dry wood for around 2 years before using it. This brings the moisture content to well under 20% (closer to 12%).
There is an argument for carbon capture in soil, but this is very difficult to achieve. Of course wood can be recycled and turned in to new products such as MDF and chipboard but the emissions of this process far exceed the emissions from burning the wood on a stove. And at some point those products will ultimately end up in landfill.
It’s interesting to look at actual sources of emissions in the UK, for example what could be causing the pollution around the Hexham area of Northumberland? Could it be connected with the giant Egger chipboard factory? Or is it all those rural wood burning stoves? I wonder…
PM2.5 emissions from wood stoves
So we’ve established that carbon dioxide isn’t the main issue. But what about all that awful smoke? Yes, that is an issue. Smoke is mostly formed from particulates of wood that haven’t been burned properly. These particles can be tiny and embed themselves in our lungs, which we obviously don’t want.
The good news smoke from fires can be almost eliminated by following a few simple steps:
- Use a modern EcoDesign wood burner
- Only burn dry wood with a moisture content well under 20%
- NEVER burn man-made materials (MDF, chipboard etc.)
- NEVER burn rubbish
- NEVER burn wet wood
- Learn how to light a fire!
Stick to nice dry hardwood on a good quality, newer stove and you should find very little smoke ever appears from your chimney. You’ll know when you have an efficient burn. The glass of the stove will be clean, there’ll be no carbon deposits inside the stove, very little ash and hardly any smoke.
Measuring emissions from a wood burning stove
As part of my research I spent quite a long time measuring indoor air pollution. To do this I used an air quality monitor with the Plantower PMS5003 sensor.
We generally measure air quality by using the PM2.5 index. In other words how many particles are there in the air that are smaller than 2.5 microns in size.
I carried out an array of tests to establish a baseline and then carried out various household activities to measure the levels of PM2.5 particulates. The results were:
|Baseline indoors – Fire OFF:||5|
|Indoor measurement – Fire ON:||5|
|Baseline outdoors – Fire OFF:||6-8|
|Indoor measurement – Fire ON:||6-8|
|Using the oven:||30|
Some of these results really surprised me. For example, even 4 hours after using a frying pan the PM2.5 reading was 35. That’s FIVE TIMES higher than the emissions from our wood burning stove.
The biggest shock was using a joss stick. Not only where the PM2.5 readings through the roof (800+) but even 5 hours later we were still getting readings of 75+. No other sources of emissions. The fire hadn’t even been on. That 15 TIMES higher than the emissions from our stove! AND this lingered in the air for well over 24 hours!
So are wood burners safe?
Modern EcoDesign stoves are more efficient than many gas boilers and the fuel source is entirely renewable. An efficient burn with dry wood generates minimal particulates. In my own tests our stove didn’t increase indoor or outdoor air pollution at all. Cooking generated far more harmful emissions. So make of that what you will.
We’re living in an age of safeism and it’s tragic to watch. A vocal minority are trying to eliminate literally every single risk from life. While I’m sure their motives are sincere, the outcomes often cause more harm than good. Cold is a much bigger killer than heat.
There’s also a LOT of hypocrisy out there along with deliberately misinterpreted data. Much of this is down to the click-bait nature of modern mainstream media.
Air quality in the UK is generally outstanding and suggesting we shouldn’t heat our homes with wood that’s otherwise destined for landfill is frankly insane. Almost as insane as the energy policies of Europe over the last 20 years.
As I write this the vast majority of UK’s electricity (56.6%) is being generated by burning gas. That’s a fossil fuel. The carbon released by burning that gas had been locked away for millions of years. We’re unlocking it.
Unfortunately we’ve put ourselves in the short-sighted situation where gas is the only option. Renewables are great but when the wind don’t blow and the sun don’t shine you need something to make up the shortfall.
It will take years to fix this mess. We urgently need many more nuclear power stations. We urgently need electricity storage capable of delivering bursts of 15+ GW when the wind don’t blow. Until then, better education about the correct use of wood burners could dramatically cut emissions.
Here are a few of the sources where I’ve managed to gather data from. Obviously bear in mind the Wikipedia articles can be edited by anyone and therefore may not always contain accurate information.