July 10, 2025 Switching to Biomass Heating
Wood heat is sometimes accused or suspected of damaging air quality with particulate matter (specifically PM10 and PM2.5). That is simply not true. Bioenergy heating technology:
- is strictly regulated by the UK government
- has advanced and sophisticated emissions filtration
- emits dramatically fewer particulates than its alternatives (like fossil fuel)
UK regulations ensure that wood heat particulate emissions are negligible
When the UK government introduced the Renewable Heat Incentive (RHI), it specified that in order for a wood heat boiler to be eligible for payments under the scheme, its emissions must bet 30mg of particulate matter per megajoule, or lower. The average of registered boilers’ particulate emissions as stated on their emissions certificates is 14.2g/MJ.
Under the Environmental Permitting Programme, the Industrial Emissions Directive, the Clean Air Act, the Large Combustion Plant Directive, and the Ecodesign Certification for Small Scale Biomass, wood heat is governed robustly, and bioenergy boilers may not be installed in the UK if they exceed acceptable levels of particulate emissions.
To illustrate that fact, here is DEFRA’s graph charting the emissions of PM10 and PM2.5 from 1990-2023. In the early years of the RHI, particularly the Non-Domestic RHI (NDRHI), there was a surge in wood chip and wood pellet boiler installations, and now there are over 17,300 non-domestic biomass boilers in the UK. The chart below demonstrates that at the height of the NDRHI’s popularity, air quality continued to improve.
Source: DEFRA, ‘Emissions of air pollutants in the UK – Particulate matter (PM10 and PM2.5)’
Some of the most advanced filtration is found in bioenergy boilers
Modern wood chip and wood pellet boilers filter their emission very effectively, and are often also fitted with electrostatic precipitation (ESP) filters that improve particulate emissions even further (up to 99%).
That is in stark contrast to systems like log burners and open fires, which are simply fires and flues with not filtration and with no regulation or control of fuel.
| PM2.5 emissions per GJ-1 | Single home biomass boiler (<50kW) | Traditional heating stove (Non Ecodesign compliant) | Open fireplace |
| Solid PM2.5 (g GJ-1) | 30 | 150 | 260 |
| Condensable PM2.5 (g GJ-1) | 30 | 650 | 640 |
Source: REA, ‘Modern Biomass Boiler and Air Quality’
Wood heat replaces fossil fuel heating, which is considerably worse for air quality
The most common use case for wood heat is in premises that are off the gas grid, and/or large and especially difficult-to-insulate buildings. Those types of premises traditionally use oil, liquid petroleum gas, or even coal for their heating fuel.
A typical oil boiler emits 50mg of particulate matter per MJ of power, and coal tends to produce 120mg/MJ. Given the average 14.2 mg/MJ of an NDRHI wood heat boiler, that is around 8.5 times lower than a coal boiler, and over 3.5 times lower than an average oil boiler.
Given those figures, even if the average wood heat boiler were twice or three times as bad for air quality, it would still represent an improvement.
Further reading
Wood heat, ESG, and particulate emissions: The facts
Bioenergy boilers and air quality
Is bioenergy bad for air quality?
Decarbonising heat and improving air quality with wood heat
Innasol, the REA, and the wider wood heat industry would welcome any opportunity to discuss our industry-leading air quality credentials with government bodies and relevant regulators.
If your business is thinking about future-proofing your energy, or if you have any questions about air quality or wood heat generally, our Guide to Green Business Energy has a wealth of information within it.
If you would like to speak to one of our UK-wide network of renewable energy experts, and get no-obligation guidance on your business’s ESG targets, 01621 892613.
