Galvanized Chimney ExtensionSuitable for all Buschbeck barbeque fireplaces. The chimney extension is primarily used to extend the chimney. The length is decisive for the draft and thus also for the ability to completely discharge smoke gases into the outside air. The length of the chimney means that the negative pressure is created and thus the exhaust gases are practically sucked outwards. If this negative pressure is not strong enough, your chimney is too short. 3 2 10 Rule