Technical Booklet L Combustion Appliances and Fuel Storage Systems·Page 28·2.31
Flue area sizing for lining
An oversized flue should be lined to reduce the flue area to suit the intended combustion appliance, as using an oversized flue can be unsafe.
The use of an oversized flue can be unsafe so a flue should be lined to reduce the flue area to suit the intended combustion appliance.
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