Technical Booklet L Combustion Appliances and Fuel Storage Systems·Page 60·4.19
Protective cage for large diameter natural draught open-flued appliances
Natural draught open-flued appliances with flue diameter greater than 170 mm require a protective cage for solid fuel use with mesh size between 6 mm and 25 mm, with total free area at least twice the flue's cross-sectional area.
A flue serving a natural draught open-flued appliance, with a diameter greater than 170 mm, should be fitted with a protective cage designed for solid fuel use, having a mesh size not less than 6 mm and not greater than 25 mm. The total free area of the cage should be not less than twice the cross-sectional area of the flue.
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