Block-off plate above smoke chamber?

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branchburner

Minister of Fire
Sep 27, 2008
2,758
southern NH
Has anyone ever seen or installed a block-off plate above the smoke chamber in a fireplace, at the actual base of the flue, as opposed to having it in the damper area? Are there any compelling reasons why this couldn't/shouldn't be done?
 
Wow - you must be Santa Claus to squeeze all the way up in there and install the plate! That is probably the main reason you don't see it done more often - just too hard to get up in there. Additionally, I think the general idea is to have the maximum amount of flex liner 'blocked off' (ie behind the block off plate) so if any disaster does occur the flames are most likely to be up in the flue instead of out in the room. Putting the plate behind the smoke shelf would expose a couple more feet of flue pipe.
 
I think I've seen somewhere a plate designed to be attached to the bottom end of the liner and the whole shebang lowered down the flue from the top. I didn't look closely at the time (some online chimney supply place), so I'm not sure how the seal between plate and flue was done... and maybe I'm mis-remembering the whole thing. But if the flue was clean (to allow installation) it seems like this idea ought to be capable of working.

I'm interested in this subject myself, since the fireplace my Jotul is direct-connected to has a vintage Heatilator-type steel liner and heat exchanger tubes, that for historical reasons I'm not eager to remove. Right now the blank-off plate for the direct connection is just below the damper throat and the heat exchanger tubes, but if I could at least line the flue that's up in the chimney, I expect I'd get better draft and less condensation/creosote up there. (I'll probably always have an unpleasant cleanout task around the heat exchanger, though.)

I'll look and see if I can find that bottom-end block-off plate.

Eddy
 
Thanks guys. What I was thinking is that instead of the steel liner connecting directly to the stove it would connect to a foot or two of stove pipe that stuck up into the smoke chamber. The plate (and insulation) would be at that connection, at the base of the existing flue tiles. This is for a freestanding stove in an existing 4x3 brick fireplace hearth.
I imagined rigging a removable rear heat shield that would fit up around the rear vent, relecting heat down and out. Once the stove was really cranking, if I wanted to drop the shield down I could let some more heat be absorbed into the rest of the ground floor masonry structure. This via all the exposed brick in the large smoke chamber (nearly 4x2x1and1/2), and without letting too much of it float up the chimney. Make any sense?
 
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