What This Requirement Covers
Biomass boilers and stoves burn wood pellets, wood chips, or logs to provide space heating and hot water. They are classified as solid fuel appliances under Approved Document J and must be installed in accordance with the same requirements for hearths, flues, and air supply as other solid fuel appliances.
Key Requirements
Installation Requirements
- A constructional hearth is required beneath the appliance (minimum 125 mm thick, non-combustible)
- A flue complying with the appliance manufacturer's requirements must be provided (typically minimum 150 mm diameter for boilers)
- Minimum flue height: 4.5 metres from the appliance to the terminal
- Air supply for combustion must be provided (permanent vent sized to the appliance's requirements)
- A carbon monoxide alarm must be installed in the room containing the appliance
Fuel Storage
- Wood pellets: Require a dry, enclosed store with mechanical or pneumatic delivery to the boiler
- Wood chips: Require a larger store and mechanical feed system; typical store size 3-5 m3 for a domestic installation
- Logs: Require a covered store with natural ventilation for seasoning; logs should be dried to below 25% moisture content
- The fuel store must be accessible for delivery and must not present a fire risk to the building
Emissions and Clean Air
- Biomass appliances produce particulate emissions; in smoke control areas, only DEFRA-exempt appliances may be used
- Non-exempt appliances may still be used in smoke control areas if an exemption is obtained from the local authority
- The Domestic Renewable Heat Incentive (RHI) was available for biomass boilers (now closed to new applicants); the Boiler Upgrade Scheme covers biomass in some circumstances
HETAS Registration
- Biomass boiler and stove installations should be carried out by a HETAS registered installer for competent person scheme self-certification
Practical Compliance Tips
- Check whether the property is in a smoke control area before specifying a biomass appliance
- Size the boiler to the heat demand of the building; oversized biomass boilers are less efficient
- Ensure adequate fuel storage and delivery access; a biomass system requires ongoing fuel management
- Install the flue to the manufacturer's specification and ensure it achieves adequate draught
- Commission the system and record the commissioning data for Building Control
- Maintain the flue and chimney annually (sweep and inspection)
- Keep the HETAS certificate, commissioning record, and appliance documentation for the building file