Technical Booklet L Combustion Appliances and Fuel Storage Systems·Page 33·2.40
Configuration of natural draught flues serving open-flued appliances
Flue systems should minimise resistance to flue gas passage by being straight and vertical where practicable, with limited horizontal sections and bends at shallow angles to allow effective operation and maintenance access.
A flue system should offer least resistance to the passage of the flue gas by minimising changes in direction or horizontal length. Where practicable the flue should be straight and vertical except for the connection to a combustion appliance with a rear outlet. The connecting horizontal section should be not greater than 150 mm in length and where bends are essential, they should be angled at not more than 45º to the vertical.
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