Natural draught flue
Approved Document J, Combustion appliances and fuel storage systems, 2010 edition incorporating 2010, 2013 and 2022 amendments, defines a natural draught flue as one in which: ‘…the combustion products flow into the flue as a result of the draught produced due to the difference between the temperature of the gases within the flue and the temperature of the ambient air. Taller flues produce a greater draught at their base. Except for those balanced flue appliances which are designed to discharge directly through the wall adjacent to the appliance, a satisfactory natural draught requires an essentially vertical run of flue.’
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