Sizes of flues for chimneys

Table 3.2 Sizes of flues for chimneys Installation(1) | Minimum flue size Fireplace with an opening of up to 500 mm x 550 mm. | 200 mm diameter or a rectangular/square section having the equivalent cross-sectional area and a minimum side dimension of 175 mm. Fireplace with an opening greater than 500 mm x 550 mm or a fireplace exposed on two or more sides. | See paragraph 3.7. If a rectangular/square section flue is used the minimum side dimension should be not less than 200 mm. Closed appliance with a rated heat output not greater than 20 kW which – (a) burns smokeless or low volatiles fuel(2); (b) is an appliance which meets the requirements of the Clean Air (Northern Ireland) Order when burning an appropriate bituminous coal(3); or (c) is an appliance which meets the requirements of the Clean Air (Northern Ireland) Order when burning wood(3). | 125 mm diameter or rectangular/square section having the equivalent cross-sectional area and a minimum side dimension of 100 mm. Pellet burner or pellet boiler which meets the requirements of the Clean Air (Northern Ireland) Order(3). | 125 mm diameter. This may be reduced to no less than 100 mm when permitted by the appliance manufacturer and supported by calculation according to BS EN 13384: 1. This calculation can be applied to an individual installation or manufacturers can provide precalculated designs. Other closed appliances with a rated heat output not greater than 30 kW burning any fuel. | 150 mm diameter or rectangular/square section having the equivalent cross-sectional area and a minimum side dimension of 125 mm. Closed appliances with a rated heat output greater than 30 kW but not exceeding 50 kW burning any fuel. | 175 mm diameter or rectangular/square section having the equivalent cross-sectional area and a minimum side dimension of 150 mm. Notes: (1) Closed appliance includes cookers, stoves, room heaters and boilers. (2) Fuels such as bituminous coal, untreated wood or compressed paper are not smokeless or low volatiles fuel. (3) These appliances are known as 'exempted fireplaces'.