Glossary · Boilers and boiler types
What is a biomass boiler?
A biomass boiler heats water for radiators and hot water by burning wood fuel such as logs, pellets or chips, instead of gas or oil. In England and Wales the Boiler Upgrade Scheme offers a £5,000 grant towards one, but only for off-gas, rural properties with an emissions certificate.
Key points
- Approved Document L lists biomass boilers by fuel: logs only, or wood pellets and chips with automatic feed.
- The Boiler Upgrade Scheme pays £5,000 towards a biomass boiler in England and Wales.
- To qualify, the property must be off the gas grid, in a rural location, and the boiler must have an emissions certificate.
- In a smoke control area, wood can only be burned in an exempt appliance, and you must use only the fuel the manufacturer says.
- Primary heating solid fuel boilers need separate time controls for heating and hot water, and automatic control of the burning rate.
How a biomass boiler works
A biomass boiler burns an organic fuel, usually wood, to heat the water for your radiators and hot water. It replaces the gas or oil boiler in a wet central heating system. The Boiler Upgrade Scheme, which funds them, is for replacing fossil fuel heating systems such as oil, gas, electric or LPG.[2]Department for Energy Security and Net Zero, Apply for the Boiler Upgrade Scheme: check if you're eligible
Approved Document L, the building regulations guidance for England, groups wood-fuelled boilers by how they are fed. An independent boiler that burns wood logs only is fed in batches. An independent boiler that burns wood pellets or chips can be fed automatically.[4]Ministry of Housing, Communities and Local Government, Approved Document L, Conservation of fuel and power, Volume 1: Dwellings, 2021 edition incorporating 2023 amendments Batch feed means the fuel is loaded in batches. Automatic feed means it is supplied without hand loading.
If a solid fuel appliance supplies primary heating as part of a central heating system, Approved Document L says it should have separate time controls for space heating and hot water, and automatic control of the burning rate.[4]Ministry of Housing, Communities and Local Government, Approved Document L, Conservation of fuel and power, Volume 1: Dwellings, 2021 edition incorporating 2023 amendments
Efficiency and rules
| Boiler category (Approved Document L) | Minimum efficiency | Feed |
|---|---|---|
| Independent boiler, wood logs only | 75% | Batch |
| Independent boiler, wood, pellets or chips, nominal load | 75% | Automatic |
| Independent boiler, wood, pellets or chips, part load | 70% | Automatic |
These are minimum figures measured on gross calorific value, set out in the guidance.[4]Ministry of Housing, Communities and Local Government, Approved Document L, Conservation of fuel and power, Volume 1: Dwellings, 2021 edition incorporating 2023 amendments The categories follow The HETAS Guide to Approved Solid Fuel, Wood and Biomass Products and Services.[4]Ministry of Housing, Communities and Local Government, Approved Document L, Conservation of fuel and power, Volume 1: Dwellings, 2021 edition incorporating 2023 amendments HETAS is a not-for-profit body. It lists appliances and fuels that meet the standards and registers trained installers and service engineers.[5]HETAS, About HETAS
Grant and eligibility
GOV.UK says the Boiler Upgrade Scheme gives £5,000 towards a biomass boiler, with one grant per property.[1]Department for Energy Security and Net Zero, Apply for the Boiler Upgrade Scheme: what you can get Ofgem, which runs the scheme, gives the same figure.[6]Ofgem, Boiler Upgrade Scheme (BUS) To get one, all of these must be true. Your property is off the gas grid, it is in a rural location, and the boiler has an emissions certificate showing that polluting emissions are kept to a minimum.[2]Department for Energy Security and Net Zero, Apply for the Boiler Upgrade Scheme: check if you're eligible You cannot get a biomass grant for a self build property.[2]Department for Energy Security and Net Zero, Apply for the Boiler Upgrade Scheme: check if you're eligible
You must own the property and be replacing a fossil fuel heating system. New build properties that are still being built are not eligible.[2]Department for Energy Security and Net Zero, Apply for the Boiler Upgrade Scheme: check if you're eligible Ofgem says installers must be MCS certified to apply on your behalf.[6]Ofgem, Boiler Upgrade Scheme (BUS) See MCS certification and our boiler grants page. Grant rules change, so check GOV.UK before you commit.
Smoke control areas
Many parts of the UK are smoke control areas. GOV.UK says that in a smoke control area you cannot release smoke from a chimney, and you can only burn authorised fuel unless you use an appliance approved by Defra, also known as an exempt appliance.[3]Department for Environment, Food and Rural Affairs, Smoke control areas: the rules Unauthorised fuels, such as wood, can only be burned in exempt appliances such as some boilers, cookers and stoves.[3]Department for Environment, Food and Rural Affairs, Smoke control areas: the rules You must use only the fuel the manufacturer says can be used.[3]Department for Environment, Food and Rural Affairs, Smoke control areas: the rules In England you may have to pay a penalty of up to £300 if your chimney releases smoke in a smoke control area, and you can be fined up to £1,000 for buying unauthorised fuel.[3]Department for Environment, Food and Rural Affairs, Smoke control areas: the rules Your local council can tell you if you are in one.
Example
Aisha has a farmhouse near Otley, off the gas grid, heated by an old oil boiler. A rural property replacing a fossil fuel system fits the grant conditions.[2]Department for Energy Security and Net Zero, Apply for the Boiler Upgrade Scheme: check if you're eligible She asks an MCS certified installer for a quote. The boiler must have an emissions certificate, and she checks with the council whether the house is in a smoke control area. If it is, the boiler must be an exempt appliance burning the fuel the maker names.[3]Department for Environment, Food and Rural Affairs, Smoke control areas: the rules
What people get wrong
A biomass boiler is not a way round smoke rules. In a smoke control area wood can only be burned in an exempt appliance, and the grant only covers off-gas, rural homes with an emissions certificate.
GOV.UK sets out both conditions.[2]Department for Energy Security and Net Zero, Apply for the Boiler Upgrade Scheme: check if you're eligible[3]Department for Environment, Food and Rural Affairs, Smoke control areas: the rules People also assume the grant covers any home. It does not. Self builds, most new builds and social housing are excluded.[2]Department for Energy Security and Net Zero, Apply for the Boiler Upgrade Scheme: check if you're eligible Check the boiler is suitable for your fuel supply and storage before you apply.
The bottom line
A biomass boiler burns logs, pellets or chips to heat a wet central heating system. In England and Wales a £5,000 grant is available, but only for off-gas, rural properties with an emissions-certified boiler fitted by an MCS certified installer. Smoke control rules and fuel storage decide whether it works for your property.
Common questions
How much is the grant for a biomass boiler?
GOV.UK says the Boiler Upgrade Scheme gives £5,000 towards a biomass boiler. You get one grant per property, and the value is taken off the amount you pay for the installation.
Who can get a biomass boiler grant?
GOV.UK says the property must be off the gas grid and in a rural location, and the boiler must have an emissions certificate. You must own the property and be replacing a fossil fuel system. Self builds do not qualify.
Can I burn wood in a smoke control area?
Only in an exempt appliance, such as some boilers and stoves approved by Defra. GOV.UK says you must use only the fuel the manufacturer says can be used. Contact your local council to find out if you are in a smoke control area.
Does a biomass installer need to be registered?
For the grant, installers must be MCS certified. HETAS, a not-for-profit body, runs a competent person scheme for installers of biomass and solid fuel heating.
Sources
We cite the original source for every figure: government, regulators, standards bodies and manufacturers' own documents. Each one shows the date we last checked it.
- Department for Energy Security and Net Zero. Apply for the Boiler Upgrade Scheme: what you can get. Checked 11 November 2026. ↩
- Department for Energy Security and Net Zero. Apply for the Boiler Upgrade Scheme: check if you're eligible. Checked 11 November 2026. ↩
- Department for Environment, Food and Rural Affairs. Smoke control areas: the rules. Checked 11 November 2026. ↩
- Ministry of Housing, Communities and Local Government. Approved Document L, Conservation of fuel and power, Volume 1: Dwellings, 2021 edition incorporating 2023 amendments. Checked 11 November 2026. ↩
- HETAS. About HETAS. Checked 11 November 2026. ↩
- Ofgem. Boiler Upgrade Scheme (BUS). Checked 11 November 2026. ↩