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Small Cabin Forum / Cabin Construction / Sealing off an old fireplace
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Eddy G
Member
# Posted: 18 Oct 2016 09:57
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There was an old fireplace in our cabin. It was in pretty bad shape but serviceable. The chimney was/is in great shape.

We had a wood stove installed in front of the fireplace (on a hearth).
The smoke pipe from the wood stove comes out the back of the stove in to the fireplace and up the chimney.

We plan to brick up the face of the fireplace around the smoke pipe.

The top of the chimney is sealed around the vent pipe where it exits the chimney and then again on the bottom where the old damper was.

My question:
Is there a way to insulate the inside of the fireplace safely before we seal it off? Obviously stuffing the hole with fiberglass or blown in insulation is big nono and a fire hazard.

I was thinking of lying rockwool on the floor and trying to attach it to the walls to keep the cold and drafts out (as much as possible).
I'm not sure how far away we have keep the rockwool from the vent pipe without burning the place down. That would be bad....

DaveBell
Moderator
# Posted: 18 Oct 2016 10:07
Reply 


Trapped air is the best insulator. Your attempting to insulate a small portion of the entire flue. Not sure it's worth the trouble. Just brick it up.

bldginsp
Member
# Posted: 18 Oct 2016 14:14 - Edited by: bldginsp
Reply 


I'm pretty sure rock wool is considered non-combustible, so theoretically the flu could contact it. But always good to have clearance around the flu to allow air to circulate a bit to avoid heat buildup next to the flu.

DaveBell- its true that confined air is a good insulator, that's basically what all insulation does. But if the air can move, or if there is any draft, you lose the insulating effect. What insulation does is hold the air and prevent it moving.

In a situation like this I'd first seal up the masonry as much as possible with trim, caulk, mortar, etc. then put a layer of rock wool in there, leaving space around the metal flu. Most double and triple wall metal chimneys require 2" clearance to combustibles, so you could use fiberglass if it's held back.

Also, if you put the woodstove on the hearth in front of the fireplace you might not have the required 16" of masonry in front of the stove. Also, the hearth in front of the fireplace is generally built on wood. If your stove is made to go on such a hearth, as most are, you are fine, but if the stove you are using is an insert that is not inserted, it could be a problem. Inserts are rated to be placed on the inside of the fireplace, where the hearth has no wood beneath it.

Eddy G
Member
# Posted: 18 Oct 2016 19:20
Reply 


The hearth is an oversized 2" granite slab on top of 1/2" mortar so no problem there...
Its a Vermont Castings Dutch west stove made to stand alone... exhaust top or back... we went out the back.

Like I said the fireplace wasn't much to look at.
Covering it up is best.

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