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Sealing stovepipe joints?

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by unit40, Sep 15, 2007.

  1. unit40

    unit40 New Member

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    Does anyone here have any opinions on whether or not to seal stovepipe joints? I have read and heard conflicting ideas. I have never sealed the joints because i thought that it was unnecessary. I just put the male end down, and secured with three sheet metal screws. If sealing is supposedly unnecessary, then why do some folks recommend it?

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  2. Todd

    Todd Minister of Fire

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    I think sealing them is a good idea. Helps improve draft and keeps smoke or gases from leaking out. I seal mine with furnace cement then screw them together.
  3. Gooserider

    Gooserider Mod Emeritus

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    Sealing is better, it does help draft which can give you a better fire. Smoke leaking out shouldn't be a concern, but air leaking into the pipe is not good. I would especially pay attention to the stove / pipe junction as most critical to seal. The other joints are important but less so. However the three screws are the most important thing.

    Gooserider
  4. elkimmeg

    elkimmeg Guest

    The most important part is to install the connector pipes correctly fully inserted. No crimping exposed installed fully tight to the rib.

    I find ,at times screws can actually strip and actually cause pushing the two connector pieces in a joint apart What e seems to work best is to pre drill them with
    a slightly smaller hole than the sheet metal screw. If really concerned about connector pipe leakage, then welded seam pipe is far superior than snap seam piping

    Especially when it comes to adjustable elbows

    Personally I add a bead of gasket cement before inserting both ends.
  5. jtp10181

    jtp10181 Minister of Fire

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    We normally use DVL (double wall) for everything, and in one case we used single wall for a out the back install into a Tee inside a masonry fireplace. The customer was complaining about poor draft. After we got the fire going you could SEE the glow from the fire through the joint between the first and second pipe. Where the seam was it flexed inward making a fairly large gap. After we sealed that up the thing worked much better.
  6. Robbie

    Robbie Minister of Fire

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    How about black pipe "high heat" tape on the outside of each joint ?

    Would this work ? Seal ? Make a mess on the outside if you have to remove it ?



    Robbie
  7. Gooserider

    Gooserider Mod Emeritus

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    NO! DO NOT DO THIS!!! Single wall stove pipe can reach several hundred degrees, much hotter than any high heat tape that I'm aware of is rated to handle. If you exceed the tape's rating, at best it will melt and make a nasty mess. It could also give you some major smoke, and possibly start a fire.... The correct method is to smear a bead of furnace cement around the INSIDE of the female connector, stick the male connector in far enough that no crimps are showing, and then install your three screws per joint.

    Note that some stoves have connector collars that have a shorter inner length than the length of the crimps on standard stove pipe (seems like a poor design to me, I don't know why they do it that way, but they do) In order to make the joint properly, you need to either get a specialized "starter" peice of pipe, or just trim the crimps on a regular pipe to be about 1/16" less than the depth of the stove collar.

    Most pipes have a bulge on the male end, just above the crimps. In a properly assembled joint that bulge should be touching the female end of the pipe it connects to.

    Gooserider
  8. EatenByLimestone

    EatenByLimestone Minister of Fire

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    This may help...

    Last year I used cheap stovepipe from Lowes. It wasn't especially round, but it worked.

    This year I went to the stove shop and picked up some of theirs, not only was it round after snapping it together, it was better quality and fit together nicer.

    Without sealing the stove pipe, I have better draft so far this year. I'll probably seal it later this year, after I'm done with short nightly burns, but the sealing will not be necessary.

    Matt
  9. DrivenByDemons

    DrivenByDemons Member

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    Sorry for the bump on such an old topic but I took apart my Double Wall to clean and you could tell where the air leaks were by the way the creosote deposited itself around the joints. The rest of the pipe was very clean. Is there a better way to seal these joints besides furnace cement? I would like to be able to take these joints apart in the future if need be and that cement seems like it fairly permanent.
  10. Gooserider

    Gooserider Mod Emeritus

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    Not really. Furnace cement is the only way that's guaranteed to handle the heat. However don't worry about it being permanent - if there is a problem with furnace cement it's that it isn't very permanent! (This is part of the reason you have to screw the pipe together as well as cement it) Refractory cement is very brittle, and doesn't adhere all that well, so if you wiggle the joint after taking the screws out, the cement will quickly and easily fracture and come apart. A lot of times you are lucky if it actually stays in place long enough to give you trouble taking it apart.

    Gooserider
  11. DrivenByDemons

    DrivenByDemons Member

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    Your talking about the stuff in the caulk tube, right??? Black furnace cement??? That stuff seems hard as hell and very durable... I used it to cement the starter pipe to my stove cause I figured I would never really need to remove that piece and I was getting some major leaking right there. You could hear it whistling. I feel like the only trouble I really have with creosote is at these damn joints.
  12. uptrapper

    uptrapper New Member

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    Do you know what brand you bought? I have been looking in the northern tool catalog at some pipe that is already put together and slides to the right length, wondering if that is good stuff to use.

    Mike
  13. mtaccone

    mtaccone New Member

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    I was wondering about the lowes crap as I just put 2 elbows together from there that self destructed as soon as I turned them. Guess I to will try the stove shop, Just though stove pipe was being made like crap justa as everything else today.
  14. stoveguy2esw

    stoveguy2esw Minister of Fire

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    ive used this and had no issues with leakage at all , it expands and contracts with the pipe and as any one who has used furnace cement it cracks beacuse its rigid and will not flex as the pipe expands and contracts.

    http://www.rutland.com/productinfo.php?product_id=28
  15. Nic36

    Nic36 Feeling the Heat

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    If you want some tough single wall stove pipe, there is the Heat-Fab 22 gauge stuff. Very thick and almost impossible to bend.
  16. Gooserider

    Gooserider Mod Emeritus

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    I agree that the silicone looks like nice stuff in some ways, but I don't think it's suitable for pipe joints on a cordwood stove, at least not close to the stove - I know that I quite regularly get my stovepipe WELL over 600*F according to my in the flue pipe thermometer - indeed 600 is not even into over-fire range. Given that we are encouraged to burn a HOT fire on a regular basis, in order to keep down creosote, I'd expect the silicone not to hold up well. It would probably be OK at locations further away from the stove - I'd have no problem using it to seal a blockoff plate to the wall of a fireplace (but would stick w/ refractory cement for the joint between the plate and the pipe) or at the top of a chimney.

    From what I've read it's fine on pellet stoves that have much lower and more controlled stack temps.

    Gooserider
  17. pinewoodburner

    pinewoodburner Feeling the Heat

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    Stove pipes can get much hotter than the 600 degrees that stuff is rated for.
  18. mountaineer79

    mountaineer79 Member

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    Question:

    If you seal with furnace cement, then take your pipes apart to clean them, do you have to remove the cement and put new cement back on? Or can you just screw the pipes back together and reuse the cement that's already there? Or can you just reapply new cement on top of the old stuff? How hard is it to pull the joints apart after the cement has set up?

    Thanks.
  19. ScottF

    ScottF New Member

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    Anytime I have used furnace cement it seems to get brittle and fall off after a while. I think it is because the metal is expanding and contracting and the cement is not. Does anyone else have this problem?
  20. Gooserider

    Gooserider Mod Emeritus

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    Yes, pretty much in the "nature of the beast"... It won't fill big gaps forever, but will seal cracks and crevices reasonably well if you have it squeezed into a joint as opposed to just smeared on top of it, and don't disturb it very much.

    This sort of applys to mountaineer79's question - when you take pipes apart, the cement that's on there will usually crumble and fall off pretty much by itself, or with minimal prodding. Just put on new stuff. If it doesn't fall off easily (unlikely), just put fresh on top of it.

    Gooserider
  21. hothead

    hothead New Member

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    I agree with Driven By Demons. I too have DVL Double Wall pipe and the only place I see creosote buildup is where the seams overlap. I will be using furnace cement to seal them in the future and see how it goes. Do not worry about separating the pipes afterwards as the cement will crumble easily once you remove the screws.
  22. MyFyrByrd

    MyFyrByrd New Member

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    What I found to work most effectively is a one or two foot length of 1/4 inch or 1/8 gasket rope (the stuff used around your stove doors). When pulled tight at the ends it's diameter shrinks quite a bit, then you can wedge it into the small gap around the stovepipe seams. Whats real nice about this is that it won't crack like cement will. plus if you can wedge it far enough into the joint (with a butter knife or something similar), it is completely unnoticeable.
  23. liplifter

    liplifter New Member

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    I'm a fabricator by trade and make alot of pipe.my next flue will be 16 ga stainless ( custom built of course) with a .125 increase over damper and there will only be 2 seams that are roped and caulked.

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