When a gas fire needs a hearth, how far the hearth extends, why its edges are marked, and how nearby combustible fabric is shielded.
A hearth and suitable shielding protect combustible building fabric from a gas fire's heat. Approved Document J, Section 3, gives guidance for England; check it alongside the particular appliance's installation instructions.
When a hearth is needed
- The default is a hearth. An appliance stands on a hearth unless every part of any flame or incandescent material is at least 225 mm above the floor, or its manufacturer's instructions say a hearth is not required (paragraph 3.40).
- Applying the height rule. Where the instructions do not settle the requirement, a wall-mounted fire qualifies for the height exception only when its lowest flame or glowing part is at least 225 mm above the floor. Below that, provide a hearth unless the manufacturer specifically permits installation without one. A glass front or a low rating is not that permission.
What the hearth is made of
- The top layer is non-combustible, non-friable material at least 12 mm thick (paragraph 3.41).
- The edges are marked, for example by a change in level. The marking warns the occupants and discourages carpet and other combustible floor finishes from being laid too close to the fire. It is a warning and a boundary: it does not hold the fire in place or protect the hearth itself from heat.
How far the hearth extends
- For appliances other than decorative fuel effect (DFE) and inset live fuel effect (ILFE) fires, the hearth surface, free of combustible material, extends at least 150 mm to each side, or to a suitably heat-resistant wall, and at least 225 mm in front (Diagram 38).
- For decorative fuel effect and inset live fuel effect fires (Diagram 37), the hearth extends at least 300 mm in front of the fire's incandescent part and, where it projects beyond the fireplace recess, 150 mm beyond each side of the recess. Use it together with the fire's instructions.
Shielding combustible fabric
- A gas appliance goes where accidental contact is unlikely, surrounded by a non-combustible surface that separates it from combustible materials (paragraph 3.42).
- For a CE-marked appliance, its instructions set the protection.
- Otherwise, use the alternative shown in Diagram 39: a non-combustible insulating shield with a fire-resistant surface at least 25 mm thick, or an unshielded air space of at least 75 mm.
- Shield thickness and air-gap width are different measurements; do not use the 25 mm shield dimension as the unshielded gap.