Trades master copy
Last reviewed: March 2026
What Part J is
Part J is the "heating kit and flues" bit of Building Regulations. It covers solid fuel stoves and fires, gas and oil boilers, flues and chimneys, hearths, air supply, and fuel storage - plus CO alarms since the 2022 update.
The aim is: appliances burn safely with enough air, combustion products get outside properly, nearby surfaces don't overheat and catch fire, oil/LPG storage is safe, and if carbon monoxide leaks, people get warned.
This guide is a summary to make Part J easier to use on site. It does NOT replace Approved Document J: Combustion appliances and fuel storage systems (current edition including 2022 CO-alarm amendments).
You must read and follow the full Approved Document J and the manufacturer's installation instructions for each appliance/flue.
This guide is written for England. Wales, Scotland and Northern Ireland have their own versions of building regulations - the principles are similar but the documents and approval routes differ, so check local requirements if you're working outside England.
Where it applies on your jobs
Part J bites on:
- Log burners, multi-fuel stoves, open fires and room-heaters.
- Gas boilers and gas fires (including new or replacement combis and system boilers).
- Oil-fired boilers and oil storage tanks.
- Flues, chimneys (new and relined), twin-wall systems, terminals and hearths.
- Any job where you're altering the room/air supply around an existing appliance (removing vents, blocking chimneys, changing windows/doors etc.).
Key "trigger points" - what matters on site
Air supply (J1)
- Every fixed combustion appliance needs enough air for safe combustion and flue operation - especially open-flued and solid fuel appliances, but also some room-sealed appliances depending on output and room size.
- Blocking up air bricks or tightening a house (new windows/doors, extra draught-proofing) can pull an existing appliance out of compliance.
Discharge of products of combustion - flues and chimneys (J2)
- Appliances must have a suitable flue or chimney safely discharging combustion products to outside air, with the right size, height, route and terminal position for that appliance.
- You can't just "tee into" any old chimney or run undersized twin-wall because it fits - flue design must match the appliance spec and Part J tables.
Protection from fire (J4) - hearths, clearances, shielding
- Hearths must be the correct size, thickness and construction for the appliance and floor type (combustible/non-combustible).
- Clearances to combustible materials (lintels, mantels, beams, walls, floors, studwork, furniture) must follow Part J and manufacturer's instructions - log burners tight under oak beams with no shielding are a classic fail.
- Where needed, you must provide shielding or construction in non-combustible materials to keep temperatures within safe limits.
Carbon monoxide alarms (J3) - 2022 changes
- Since October 2022, when you install any fixed combustion appliance in a dwelling - solid fuel, gas or oil (excluding gas cookers) - you must provide a carbon monoxide alarm in the room where the appliance is located.
- Alarms must comply with the relevant BS EN 50291 standard and be correctly located as per Part J guidance and the manufacturer's instructions.
- This applies to new or replacement appliances in new and existing homes - not just log burners.
Oil and LPG storage (J6, J7)
- Oil tanks over 90 litres and external LPG storage serving fixed appliances have separation and fire-protection requirements - distances to buildings/boundaries, supports, fire resistance where needed.
- Oil tanks must also be installed to reduce pollution risk, with notices explaining what to do in case of leaks.
Quick reference table - common jobs
Install a new wood-burning stove in a living room
- Flue must be correctly sized, lined/twin-wall as required, with correct height and terminal clearances per Part J and stove manual.
- Hearth size, thickness and projection must suit the stove and floor type; clearances to combustibles must be met or shielding provided.
- A CO alarm to BS EN 50291 must be installed in the same room as the stove.
Replacement gas boiler (combi) in a kitchen
- Flue route and terminal position must meet Part J and boiler manufacturer's clearances to openings, boundaries, balconies, etc.
- Room-sealed boilers need correct flue and condensate termination; don't assume old hole = OK.
- A CO alarm must be installed in the room with the boiler when fitting a new or replacement fixed gas appliance.
New open fire in existing chimney
- Chimney must be checked and, if needed, lined to suit the appliance; gather and flue sizing must meet Part J and the fire manufacturer's spec.
- Hearth and recess must be correctly built and protected, with adequate clearances.
- Flue inspection openings and notice plate must be provided.
External oil tank for a new boiler
- Tank location and supports must meet separation distances from buildings, boundaries and combustible surfaces.
- Pipework and fire-protection around the tank/route must follow Part J and OFTEC guidance.
- Pollution-prevention and information notice requirements must be met.
Making a house "more airtight" around an existing appliance
- Changing windows/doors, blocking vents or sealing chimneys can affect air supply and flue performance.
- Existing appliances may need reassessing for ventilation and flue adequacy - don't just seal everything and hope.
Routes to compliance for trades
Use Approved Document J and manufacturer instructions together
Part J gives the baseline rules (air, flues, hearths, clearances, CO alarms, storage). The manufacturer then adds appliance-specific details.
Build to both - if the instructions are stricter than AD J, follow the stricter route.
Use competent installers and schemes where appropriate
- Gas appliances should be installed by Gas Safe-registered engineers; oil appliances by OFTEC or equivalent; solid fuel often under HETAS or similar schemes.
- Even when a competent person scheme is used, Part J still applies - the scheme just handles sign-off/notification.
Always include CO alarms with new or replacement fixed combustion appliances
If you're fitting a new or replacement fixed solid fuel, gas (except cookers) or oil appliance in a dwelling, budget for and fit a compliant CO alarm in the room, correctly located.
This is now standard - don't treat it as an optional extra.
Coordinate with other Parts
- Flues and hearths interact with Part B (fire safety), Part C (damp and penetrations), and Part J itself on clearances and fire spread.
- External terminals and oil tanks can also bump into Part L (efficiency) and planning/fire access in some layouts.
Who is responsible for what
On a typical domestic project:
- The designer/heating engineer is responsible for selecting the right appliance, flue route, chimney/twin-wall design, and any oil/LPG storage layout that complies with Part J.
- The installer (Gas Safe, OFTEC, HETAS, or competent person) is responsible for installing the appliance, flue, hearth and CO alarm exactly to Part J and the manufacturer's instructions.
- The builder/main contractor is responsible for making sure the surrounding construction (chimneys, openings, hearths, penetrations) is built correctly and not later compromised by other trades.
- The client/owner lives with the safety risk if it's wrong, and the legal responsibility to keep CO alarms in working order once you've installed them.
Blunt version:
If you squeeze a log burner under a timber beam, bodge a flue through the roof, or forget the CO alarm on a new boiler, you're gambling with people's lives as well as Building Regs. "We've always done it like that" won't hold up when an inspector or coroner gets involved.
Simple rule to drum into your team
If you're installing or altering any fixed combustion appliance, flue, chimney, hearth or oil tank, treat it as a Part J job. Check air, flue, fire clearances and CO alarms before you sign it off.
On-site checklist (Part J)
Before you start
- Confirm appliance type, output and fuel; get the manufacturer's installation instructions.
- Plan the flue route, terminal position and hearth/clearances in line with Part J and the manufacturer's data.
- Confirm whether it's a new or replacement fixed combustion appliance and note that a CO alarm will be required in the room.
While you're working
- Install flues/chimneys/twin-wall to the correct size, height, clearances and supports.
- Build hearths and recesses to the right dimensions and materials; protect adjacent combustibles.
- Provide required combustion air openings and don't block existing vents without an alternative provision.
When you finish
- Fit and test a suitable CO alarm in the same room as any new/replacement fixed combustion appliance (except gas cookers), positioned as per guidance.
- Check flue draw, spillage and operation in line with the appliance instructions.
- Affix any required notice plates for hearths, flues and storage systems in a visible, permanent location.
Sources
Based on:
- Approved Document J: Combustion appliances and fuel storage systems (2010 edition with later amendments, including 2022 CO-alarm changes).
- Planning Portal, LABC and industry summaries of Part J requirements for solid fuel, gas and oil appliances, flues, hearths, and fuel storage.
- Local-authority and trade guidance on CO alarm requirements from October 2022 onwards (J3), including which appliances trigger alarms and where to site them.
This guide was last reviewed March 2026. SiteKiln does not provide legal, financial or tax advice. All content is for general information purposes only. Always seek professional advice for your specific situation.
Know someone who needs this?
Working in Wales? The building rules are different. See our Working in Wales guides.
Working in Scotland? Building standards work differently. See our Working in Scotland guides.
Working in Northern Ireland? The system uses Technical Booklets. See our Working in Northern Ireland guides.
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