How to seal flue pipe to register plate.

Register plates sit at the base of the stack, where there is no liner, and are designed to prevent any gases and debris escaping into the room.

They are a requirement under the building regulations.

A closure plate however is different. Where you have a flue liner lining your chimney, you may well have or want a plate, that prevents any debris in the void falling down into the room.
In either case, the flue pipe will need to connect to the register or closure plate.

There should be a spigot into which the pipe can be fitted and jointed, if not, it should be possible to fit a plate with a spigot. 

You'll need to measure the pipe carefully and cut to size if necessary. The joint should be made gas tight with fire cement and rope seal.

Next: Preventing chimney flue fires.

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