Woodburning stove expansion causes stove pipe movement

[Tim Streater]

Our new stove expands as it heats up, and so pushes its stove pipe up. This pipe then slides a bit up the connector pipe that's built into, wossit called, the horizontal plate that seals the chimney.

Now, this has been a small problem because the stove was slightly misplaced [1] so the stove pipe was a tiny amount off-vertical, so when the stove cools, the pipe stays up there due to friction and cracks the stove cement that seals the bottom of the stove pipe to the top of the stove.

So far we've just pulled it down again when the stove has cooled off. Today the installer came over and adjusted the stove position, added new stove cement at the stove/stove-pipe join, but more crucially, put a self-tapper through the stove-pipe and connecting pipe.

Now, is such a screw a good idea? Seems to me the stove will continue to expand when hot, and now its stove-pipe and the connecting pipe can no longer slide one past the other, this expansion (of a few mm) is gonna flex the horizontal plate.

Will that give me problems? I can always take the screw out, but I wondered if that's what everyone has.

[1] Our hearth is now shiny black granite, so there may be a tendency for the stove to be moved a little in ordinary use.

[harryagain]

Well if it could move up into the plate before, it still can now. I don't see a problem.

[Tim Streater]

It wasn't moving the plate up before. It was sliding up around the connecting pipe that's built into the plate. But because it was off-vertical, there was increased friction between the two pipes, so that the weight of the stove-pipe plus the stove cement was not enough to pull down the stove-pipe when the stove cooled down and hence contracted.

[David WE Roberts]

Seems more logical to make sure that the base of the pipe is firmly fixed to the top of the stove. Might have problems with the self tapping screw and cast iron, though. Hmmm....top exit for the pipe, not rear exit? The plate in the chimney is called IIRC the register plate. Not clear quite where this self tapper is. Is it in a collar that sits in the register plate, through which the vertical stove pipe passses?

[Tim Streater]

Quite so.

I don't think the stove-pipe is cast iron but I could be wrong.

Top exit.

Ah thanks.

The register plate has, built into it, a fixed pipe that protrudes vertically down about 6" and presumably up 6". Above the plate it will have the flexible chimney liner slid over it. The above part is of course not visible.

The stove-pipe goes vertically up from the stove and slides around the downwards protruding pipe; the stove-pipe doesn't go through the register plate. So the stove-pipe can move relative to the fixed protruding pipe. So, f'rinstance, to move the stove out of the fireplace, I'd break the fire cement seal, slide the stove-pipe up completely and then have SWMBO hold it there while I moved the stove out. The stove-pipe can then be slid down and off the connecting pipe.

The self-tapper is near the top of the stove-pipe and so in about the middle of the downwards protruding section of the pipe fixed in the register plate. Without the self-tapper I would suppose that the stove-pipe can just move up and down a few mm with expansion and contraction of the stove as the stove heats up and cools down.