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Adding height to masonry chimney questions

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by senorFrog, Sep 18, 2006.

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  1. senorFrog

    senorFrog New Member

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    To those who followed my other post, going straight up off stove isn't going to work because of cost. Also, converting existing masonry chimney to class A would be cost prohibitive as well. I need to add some height to resolve draft and wind issues.

    What is the maximum height for a freestanding masonry chimney without bracing? Currently, it comes about six feet off a flat roof. How much higher could I go without bracing it? I'd like to add about four more feet. It is the 15.5 inch x 7.5 inch masonry blocks that are used with a 8 inch x 8 inch clay liner. I attached a pic. I added two more feet to what you see in this pic.

    Also, when determining the minimum required height for a chimney, do you factor in the vertical rise your double wall stove pipe adds? I.e. If My chimney is only 9 feet high from where the stove pipe enters to the top, but I have a vertical rise of 2 feet with the stove pipe, then I'd only need to add 3 more feet to the chimney for overall height of 14 feet.

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  2. MountainStoveGuy

    MountainStoveGuy New Member

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    I belive you can add a anchor plate and snap class A ontop of the masonry. Then you can buy a windbeater or vacu stack cap to help combat wind even more. if you go to duravent.com , download there catalog, and you will see what a anchor plate is.
  3. senorFrog

    senorFrog New Member

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    Sounds like an interesting solution. Not sure I'd like the aesthetics. Would that be up to code? I.e. combining masonry and class A? How high could I go with class A and not brace it? The masonry blocks would seem to be inherently stronger because of weight.
  4. MountainStoveGuy

    MountainStoveGuy New Member

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    astectilcy, it would not look as good. no. finacially it might be less expensive. yes, anchor plates are used for this purpose, and yes i think you would have to brace it. In case you didnt find the catalog here it is
    http://www.duravent.com/docs/Catalogs/L930.pdf
  5. Marty

    Marty Feeling the Heat

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  6. MountainStoveGuy

    MountainStoveGuy New Member

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    there ya go, great suggestion marty. That would work and look good too.
  7. senorFrog

    senorFrog New Member

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    It's def something I'll look into.

    Anyone have an idea re my orig questions?

    1) How much higher can I go without bracing it?
    2) Does stack height = chimney height + stove pipe rise height?
  8. Rhone

    Rhone Minister of Fire

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  9. senorFrog

    senorFrog New Member

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    Yeh, I do need something to help with the wind. I think I need to add some height too based on comments from my other thread.
  10. Marty

    Marty Feeling the Heat

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    I am no expert. But as to #2 I would think you could measure from the top of your stove to the top of the pipe at the top of the chimney.
  11. berlin

    berlin New Member

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    lay about 5 or six more block and you'll be fine, don't worry about bracing unless you're going much higher than that. use masonry, you'll be out less than $100 and about 2 hours of work; super simple job. just going higher will probably resolve your wind issues as well.
  12. Rhone

    Rhone Minister of Fire

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    Well, figuring out the top height is tricky. Any exposed flue does not count as chimney height, neither does any uninsulated liner. Such was my case, my rigid uninsulated liner was sticking out about 24" beyond the top of my chimney. Since it wasn't Class A or insulated, the extra height was useless for helping draft. If anything, it probably was worse because that slowed the draft right down for the last 20" or so being exposed like that. Like those who have their flue tiles sticking way out beyond the crown of their chimney, that extra height is useless to help draft, it has to be enclosed in the chimney.

    I purchased an extend-a-flue this weekend, once you see the build that should explain the price. It's built like a tank, my wife couldn't lift it off the ground when it was put together. I like that it seperates so you can bring it up easily, trying to get it up in one piece would be difficult. The cage is awesome, keeps animals out and you align and twist to put on, and twist and align to remove. Makes cleaning a snap, no drill up the ladder needed. My wife and I were impressed with the quality and look. I'll tell you how it goes when I install it. Once my stainless 30 I ordered from my local shop 3 weeks ago comes in, I can find out how much rigid I need, order that part, and finish the installation with an extend-a-flue. I think it was the best answer to heightening my chimney, particularly since my chimney has more than one flue.
  13. Roospike

    Roospike New Member

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    Marty is correct. Its from the top of your stove to the top of the pipe ( not the top of the cap ) For the metal A chimneys it states if your pipe is 4' and over it needs braced. Unsure with your style and unsure with how your going to add more height , it would depent on how your going to extend the chimney.
  14. Rhone

    Rhone Minister of Fire

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    Roo, if I have an uninsulated liner sticking out 48" out the top of my chimney my draft should be awesome? My chimney sweeps told me I needed it cut back, it's one of the reasons for my poor draft because cooling is taking place within the exposed section, causing my draft to cool and slow down at the end causing a back-up in the rest of my liner. Made sense, and that exposed part had the most creosote, though generally the furthest parts generally do anyway. My liner instructions say that I am to cut back any excess liner beyond 4" sticking out my chimney or insulated liner. I don't know why it would say that if exposed liner was beneficial beyond the 4".
  15. senorFrog

    senorFrog New Member

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    I want to extend it by doing this. But I'd only add about 3 blocks which is 2 feet. If I only have wind problems after that I'll add a wind beater. If I find I need more height I'll ad an extend-a-flue.

    Elk, any comments on this? I was hoping you'd chime in. Especially re the calculation of stack height. (Does stack height = chimney height + stove pipe rise height (even if 45 deggree run is involved).
  16. Marty

    Marty Feeling the Heat

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    I would guess... again... that you would vertical height difference rather than pipe length.
  17. senorFrog

    senorFrog New Member

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    Yeh, that's what I mean, the rise, not the length of the pipe involved to get there.
  18. zzr7ky

    zzr7ky Minister of Fire

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    Hi -

    I'm in the process of adding 6 feet. I added 4' of masonry. I'm capping with an anchor plate, adding 3' of Selkirk Class A, and a cap. All told I'll have 17' above the flue collar. The brick and all materials was <$250. I added the Class A so I can pop it off and clean with a ladder that I can actually lift.

    I'm also planning to insulate the liner.

    I'll let you know how it drafts in a couple weeks.

    ATB,
    Mike P
  19. elkimmeg

    elkimmeg Guest

    Providing you have that chimney on solid footing it can extend 8' without additional support.

    Most pre mixed motar is junk buy a bag of pure motar and add a slovel to the premix 1 in 4. To strenghten that mix, or you be
    Back re-doing it in a fews years
  20. Roospike

    Roospike New Member

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    Rhonemas ............I have no idea what your talking about , i think your in another world there brother. Re read my post and also less coffee after 5:00 p.m.
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