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Insulation around woodstove chimney

davidmeiland | Posted in Energy, Heating & Insulation on August 6, 2007 12:18pm

Trying to figure out how best to do this…

I have a Metalbestos round woodstove chimey going thru the roof of my shop, 12/12 framed with 2×12. It is appropriately clear of all framing and sheathing (2″ is the stated clearance from the manuf). My first thought is to block carefully around the pipe and then ask the insulator to stuff rockwool into the space, probably just around the bottom because at the top it opens up into the space within the roof jack. I don’t know if there’s a better detail, and this is the first woodstove I’ve dealt with, ever.

Haven’t looked in the Metalbestos catalog yet for appropriate parts, but will do so. All I’ve bought so far are the pipe, adjustable roof slope hanger, roof jack, etc.

What say ye from cold, wood-heat areas?

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  1. Piffin | Aug 06, 2007 12:29am | #1

    do Not stuff anything into the space. The hangers, supports, and spacers are all mnade specificly to maintain that 2" of space with no combustibles.

    I have dealt with two house fires where somebodyu thought they could stuff it.

    Even though it seems like the material itsself can be non-combiustible, it ccan atract and harbor lint and dust that can flash burn from the heat of a chimney fire, then smolder long enough to start the framing burning.

     

     

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    1. davidmeiland | Aug 06, 2007 12:46am | #2

      I'm not surprised you say that. Been to some house fires caused by chimneys myself. One of them was my Personal Scariest Moment.

      Just looked thru the Metalbestos catalog, which is a 35 page PDF. There really aren't any insulation baffles or anything to address this. The parts they offer consist of a trim plate that goes against the bottom of the ceiling, to cover the hole in the rock, and then an adapter from their pipe to singlewall smoke pipe.

      So I guess my solution will be a semi-kluge of wood blocking around the pipe so the insulator can go around the outside of it. I need to preserve my vent path from eave to ridge. The area around the pipe will be an air/heat leak, I guess.

      1. Piffin | Aug 06, 2007 12:56am | #3

        Look again at the parts.A ceiling support has the cieling trim but also a shield that is a larger diameter than the pipe and stands 6-8" up into the insulation space of a typical flat cieling. When insulation is lofted deeper, you need to use metal to extend that - easy to do by cutting some coil stock and slipping inside the shield.For a cathedral type ceiling, the installation is a square support box that is 14.25" square and gets nailed to the rafters.Since this is a shop, I suspect that maybe you have the metalsbestos running all the way up without a support box of ny kind needed and that would explain why you are not seeing the shielding. Maybe I need to re-read your OP 

         

        Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

  2. Waters | Aug 06, 2007 02:17am | #4

    I have personal experience with a 2" clearance ignition.

    I was working with my father building the house they lived in for 20 yrs after I left for school.

    It was winter and we were sheetrocking.  He had a big wood-fired heating unit roaring down in the basement.  This stove vented with 8" metalbestos pipe.

    We took a break and I was smelling woodsmoke...  I looked up at where the chimney passed thru the bare sheetrock ceiling, framed up thru inside a closet, and there was a glow in the attic crawlspace.

    The access was in the same closet and I nudged the door off the opening and there was a pretty good fire rippin' up there in the trusses!!

    HOLY CRAP!!

    "GET UP THERE!!" My dad screamed at me as only you would order an 18 year old to put your house fire out and I clambered up through the studs and into the attic.  All he had was a 1 gallon thermos at hand which he tossed up.  I splashed it on and it, of course, did nothing.

    He'd had loose insulation blown in--of ground up newspaper and a fire retardant as I recall and it was actually slowly burning along with the truss webbing.

    I started kicking the insulation around and it smothered the fire enough to put it out.  I came down choking and sputtering for a breath and we spent the next couple of hours making sure it was all dead out...We got the hose and sprayer up there after I'd kicked it down with the insulation itself.

    The culprit was wads of fiberglass bat insulation stuffed against the metalbestos pipe where it went thru it's box in the ceiling.  I remember it was glowing hot and blobby when we plucked it away from the pipe.

    We were minutes from going for a burger at "Tom's Tap" down the road...  would have been sittin' there hearing the sirens and thinkin, "Huh... somethin's on fire!"

     

    1. Piffin | Aug 06, 2007 02:49am | #5

      I took a look ( took a whikle to download) at the catalouge. I guess metalbestos no longer has that box option. They have a rooftop support that looks like a couple of small wings that attach to the pipe and lay out on the roof sheathing and there is no rafter shield. I see there is a part they call an atic insulation shield that you would have to trim to the pitch of the roof to use.The box I was describing is from Simpson Durashield - the triple wall folks if you have a dealer for that line in your area. 

       

      Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

      1. User avater
        Sphere | Aug 06, 2007 02:58am | #6

        I had Grant make me a Chim support box, I ran into the same problem of an OEM not existing. It is nailed to the flat bottom of the "chase" I framed, and that flat is the base of a pyramid formed bythe cathedral rafters, and the junction of the chase.

        The copper box looks cool with a black trim ring around the pipe cut out, and I left the box hang below the sheetrock about 2". 

        1. Piffin | Aug 06, 2007 03:21am | #7

          I think the stock ones hang down about 4-5" 

           

          Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

        2. Piffin | Aug 06, 2007 03:22am | #8

          You could just frame this blocking between rafters to keep the insulation back from the pipe 2" 

           

          Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

          1. davidmeiland | Aug 06, 2007 05:59am | #9

            I blocked around it with some leftover 1-1/8" ply that's about 2-1/4" clear of the pipe on all sides. In the pic you can see a rafter with romex on the side of it. Cutting across bottom right you can see the next rafter. There is a top plate for a partition in between, the wall behind the stove. The insulator will be able to blow into the area beside and above the pipe, but he'll have to work hard to get baffles in there.

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