Gas fire closure plate and catchment space checks

An inset gas fire in a builder's opening depends on parts the customer never sees. Check them before the flue-flow and spillage tests.

1. Confirm the chimney is suitable, sound and clear. Sweep a chimney that last served a solid-fuel fire: old soot and debris can fall and block the new fire's flue.
2. Confirm a closure plate is fitted where the appliance requires one. It seals the builder's opening so the fire and flue work correctly. It is not a flame guard, a gas isolation device or a heat shield.
3. Check the plate is the size and type the manufacturer specifies, in sound condition and sealed at its edges.
4. Check the spigot aperture and any specified relief opening are clear, with no opening blanked or wrongly added. An altered arrangement can impair flue performance and allow products to spill into the room; verify the installation against the fire’s instructions.
5. On an unlined brick chimney, confirm the debris catchment space below where the flue gases enter the chimney. Approved Document J asks for at least 250 mm depth and at least 12 litres volume, accessible for clearing, for example by removing the appliance.
6. Inspect the catchment space and clear any soot, mortar or debris. Without enough space, falling debris builds up on the closure plate or around the flue spigot, gradually restricting the flue and eventually causing spillage.
7. Separate the general chimney provision from the fire’s own instructions. Approved Document J exempts lined flues, flue-block flues and factory-made metal chimneys incorporating a flue box from its 12-litre/250-mm debris-space provision. The appliance may still require a cavity to collect debris and specified clearance behind its spigot, including on a lined chimney.
8. Where an old masonry chimney is oversized, porous or in poor condition, a suitable liner gives a sound, correctly sized flue path. A liner still needs checking: inspect and test the completed flue.
9. Carry on with the flue-flow check and then the spillage test before the fire is left in use.

One maker's figures: the BFM Gosford Plus

Each model's instructions add figures of their own. This inset live fuel effect fire's instructions show the kind of detail to look for:

• Flue: circular flues at least 125 mm, and every flue type at least 3 m in effective height.
• Restrictor baffle: may go in a conventional chimney or a 175 mm flue to cut the flue flow and raise efficiency, but never in a 125 mm lined flue or flue box. Every permitted arrangement still needs a satisfactory spillage test; passing one does not permit a baffle in an excluded flue.
• Opening: 400 to 450 mm wide and 550 to 570 mm high. A larger opening is reduced with a non-combustible surround sealed to the fireplace, and a proprietary surround is rated to at least 150 °C.
• Installation depth and debris space: a brick-built chimney needs room for the fire and 12 litres of debris. At an opening width of 400 mm, the manual gives 298 mm from the front of the opening to the back wall; at 450 mm wide, it gives 269 mm. This horizontal measurement is separate from the general 250 mm vertical depth below the flue-gas entry.
• Metal flue box: at least 300 mm deep, 580 mm high and 400 mm wide inside, with at least 50 mm of non-combustible mineral wool on its top face and a non-combustible base at least 12 mm thick.
• Before fitting: the chimney serves one fireplace, dampers come out or are locked open, a chimney used for other fuels is swept, any under-floor air supply to the fireplace is sealed off, and a smoke pellet shows an up-draught with no smoke leaking through the structure, upstairs rooms included.

For the gas-entry seal, LPG over-pressure protection, annual service and a worked shelf-clearance example, read Gosford Plus installation and service checks.