HETAS Installer Rules — England and Wales (2026)

The regulatory framework

England and Wales both use Part J of the Building Regulations 2010, but publish separate Approved Documents: England’s current edition incorporates 2022 amendments and Wales’s incorporates 2024 amendments. For eligible work in either nation, HETAS Competent Person Scheme notification can take the place of a separate Local Authority Building Notice. The five core J requirements are:

• 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

Official sources: England Approved Document J and Wales Approved Document J.

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 in England and Wales

The national Approved Documents size vents by appliance type and design air permeability rather than using house age as the legal test. For a typical closed stove without a draught stabiliser:

• Air permeability above 5 m³/(h·m²): provide 550mm² of permanent vent area for each kW above 5kW
• Air permeability at or below 5 m³/(h·m²): provide 550mm² per kW of the appliance’s full rated output
• Flue draught stabiliser fitted: Table 1 uses the larger 300mm²/kW for the first 5kW plus 850mm²/kW above 5kW in a leakier dwelling, or 850mm²/kW for the full output in a more airtight dwelling
• Direct external air: room-sealed or directly ducted appliances can reduce room draughts, but the installer must still follow the appliance instructions and Approved Document minimums

Commissioning tests

The installer must commission the appliance and flue in line with the applicable national Approved Document, manufacturer instructions and HETAS scheme rules. The checks include:

• 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 under the applicable English or Welsh Approved Document J
• 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: for notified work in England and Wales, HETAS says this is posted within 2 weeks and retained on its 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 safe, stop using the stove. Contact HETAS about work by one of its registrants and contact the relevant building-control or building-standards authority for your nation. HETAS publishes its complaints process and any inspection charge directly.

Frequently asked questions