Fireplaces, chimneys and flues

6.8.9Gas – combustion air

Installations shall be provided with an adequate supply of combustion air.

Table 3: Combustion air to gas appliances

Gas(1) up to 70kW input
England, Wales and the Isle of ManOver 7kW input, 500mm²/kW
ScotlandAs BS 5440-2 (as England and Wales)
Northern IrelandUp to 8kW rating, 450mm²/kW
Over 8kW, add 450mm²/kW for each kW above 8kW


1 Decorative fuel effect gas appliances should have a provision for combustion air complying with the relevant part of BS 5871 and relevant building regulations. (Generally, a minimum of 10,000mm²/kW of purpose-provided ventilation is required. Air vents should be direct to the external air or to an adjacent room or internal space, which has an air vent or vents to the external air of at least the same free area. Air vents should have an aperture dimension no smaller than 5mm.)