HETAS Installer Regulations — What Your Installer Must Do (UK 2026)

The regulatory framework

UK log burner installations are "controlled work" under the Building Regulations 2010, governed by Approved Document J (Combustion appliances and fuel storage systems). A HETAS-registered installer's self-certification under the Competent Person Scheme covers compliance with the five core J requirements:

• J1 — Air supply: permanent ventilation adequate for clean combustion
• J2 — Discharge of combustion products: flue and chimney sized and routed for safe venting
• J3 — CO warning: alarm compliant with BS EN 50291 in the room with the appliance
• J4 — Protection of building: hearth dimensions, clearances, insulation
• J5 — Information: durable notice plate showing the installation specification

Pre-installation checks

Before any work starts, a HETAS-registered installer must verify:

• Chimney condition: structurally sound, swept clean, and (if reusing existing liner) passing a smoke test
• Flue size: not smaller than the appliance outlet (typically 125mm/5" or 150mm/6" for solid fuel stoves under 20kW)
• Hearth condition: meets minimum 840×840mm freestanding dimensions, 12mm thickness (superimposed) or 125mm constructional, with adequate clearance to combustibles
• Room ventilation: assessed against appliance kW and building airtightness — permanent air vent fitted where required
• Clearances to combustibles: checked against manufacturer's data plate or default Part J distances
• Smoke Control Area status: if applicable, appliance must be DEFRA-exempt
• Ecodesign compliance: for new appliances, evidence of 2022 Ecodesign certification (or pre-2022 manufacture for second-hand)

Key Part J dimensions

• Hearth: minimum 840×840mm freestanding; extends ≥300mm in front of door, ≥150mm beyond stove sides and rear
• Flue height: minimum 4.5m from top of stove. Termination ≥600mm above ridge (if within 600mm horizontal); elsewhere ≥2,300mm horizontal from any weathered surface and ≥1,000mm above intersection
• Single-skin flue clearance: ≥3× pipe diameter from combustibles (e.g. 150mm pipe = ≥450mm clearance)
• Twin-wall flue clearance: per manufacturer specification (typically 50–60mm)
• Combustible distance through masonry: ≥200mm between flue surface and any combustible structural element
• Default stove clearance (no manufacturer data): ≥150mm rear/sides, ≥300mm front

Ventilation requirements

• Pre-2008 home, stove ≤5kW: usually no dedicated air vent required
• Pre-2008 home, stove >5kW: permanent vent providing 550mm² per kW above 5kW (e.g. 8kW stove needs 1,650mm² vent)
• Post-2008 home (airtight construction): additional vent likely required regardless of output. Highly airtight builds (air permeability ≤5 m³/h.m²): 850mm² per kW from 5kW upwards
• Room-sealed alternative: stoves with direct external air supply (Ecodesign-Ready closed-combustion models) don't need a separate room vent

Commissioning tests

Required under Approved Document J Appendix E and HETAS Technical Bulletin #10. The installer must complete and document:

• Smoke test: smoke pellet or equivalent confirms flue draw direction and detects leaks at all joints
• Spillage test: checks combustion products are not spilling into the room with the stove operating under typical conditions
• Flue draught test: manometer reading; most manufacturers require at least −12Pa. Smoke testing alone isn't enough — draught can appear adequate at as little as 4Pa
• CO alarm verification: alarm tested and correctly positioned per Approved Document J §3.41
• Notice plate fitted: durable plate near the appliance or meter recording flue/chimney specification
• Consumer handover: briefing on fuel quality, operation, maintenance, air vent function, and emergency procedures; commissioning form signed by consumer

Documentation issued

• HETAS Certificate of Compliance: posted within 2 weeks, also archived on HETAS's central database. See our certificate guide
• Commissioning document: separate from the certificate; one copy for installer, one for consumer
• Manufacturer documentation: stove manual, warranty registration, technical data
• Notice plate: durable, mounted near the appliance or meter

If the installer skips a step

Common failures HETAS inspectors find when investigating complaints: missing CO alarm, undersized hearth, inadequate flue height, missing notice plate, no commissioning document. All are grounds for HETAS to require remediation or remove the installer from the register.

If you suspect your install isn't compliant: don't use the stove. Contact HETAS at info@hetas.co.uk for a paid inspection (£150–£400 depending on complexity), and ask Trading Standards to investigate.

Frequently asked questions