What This Requirement Covers
When a new heating appliance is connected to an existing chimney, the chimney must be assessed to confirm it is suitable. Approved Document J requires that the chimney or flue is adequate for the appliance in terms of size, condition, and performance.
Key Requirements
Chimney Assessment
Before connecting a new appliance to an existing chimney
- The chimney must be swept and inspected (visually and, ideally, by CCTV)
- A smoke test or pressure test must confirm that the chimney is gas-tight (no leakage into other rooms or into the cavity)
- The chimney must be the correct size for the appliance (minimum 125 mm diameter for most stoves)
- The chimney must be free from obstructions, cracks, and damaged mortar joints
When a Flue Liner Is Required
- If the existing chimney fails the smoke or pressure test, a new flue liner must be installed
- Flue liners for solid fuel appliances must be stainless steel (grade 316 or 904L) compliant with BS EN 1856-2
- Flue liners for gas appliances may be stainless steel or flexible aluminium (where approved by the appliance manufacturer)
- The liner must extend the full height of the chimney from the appliance connection to the terminal
Disused Chimneys
- Chimneys that are no longer in use should be ventilated at the top and bottom to prevent condensation and damp
- A ventilated cap or cowl at the top allows air circulation while preventing rain entry
- An air brick or vent at the fireplace opening allows air to circulate through the flue
- Do not seal both ends of a chimney; trapped moisture causes damp and deterioration
Carbon Monoxide Protection
- A carbon monoxide alarm must be installed whenever a new appliance is connected to a chimney
- The alarm should be in the same room as the appliance, on the ceiling or at head height
Practical Compliance Tips
- Always sweep and inspect an existing chimney before connecting a new appliance; blockages and damage can cause carbon monoxide poisoning
- Commission a CCTV inspection if the chimney is old or its history is unknown
- Use a HETAS (solid fuel) or Gas Safe (gas) registered installer to assess the chimney and connect the appliance
- If a flue liner is needed, ensure it is the correct grade of stainless steel for the fuel type
- Ventilate disused chimneys rather than sealing them; this prevents damp problems
- Install a carbon monoxide alarm even if you believe the chimney is sound; it is a cheap, life-saving precaution
- Keep the chimney inspection report and flue liner certificate for the building file