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How to build chimney chase

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by FLINT, Feb 3, 2010.

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  1. FLINT

    FLINT Feeling the Heat

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    ok, so the next step of my planning process, is thinking about the new chimney.

    my friend gave me many sections of his almost brand new metalbestos 6" class A stainless chimney - I have more than enough to build mine with.

    The chimney will be in the middle of the house directly above the stove - and will start at the ceiling - with stove pipe connecting from the stove to it.

    Where can I get some good information on how to build a chase? does it start at the ceiling level or roof level?

    Could it be open to the room at the bottom so to better keep the chimney warm and improve draft?

    is this even the correct forum to ask this question?

    Thanks!!!!

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  2. John_M

    John_M Minister of Fire

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    flint, this thread will probably be moved to the DIY forum. A quick answer though: If the chimney goes through living space above the ceiling it must be enclosed (chased). If there is no living space above the ceiling the chimney need not be enclosed. In either case, when enclosing the chimney, the 2" minimum clearances to combustibles must be maintained.

    Assuming there is no living space above the ceiling, the chase would start where the chimney exits the roof. If the chimney exits the roof through a slanted part of the roof, a simple pre-fabricated metal flashing might be all that is needed. Be aware of the 3'X10' code requirement for chimney exposure above the roof. If the chimney exits the roof directly through the ridge, as mine does, the chase would be centered on the ridge. This construction can be just a little tricky, might require some engineering work/approval if a ridge beam is involved, and will require some knowledge about proper flashing to keep out blowing rain.

    Others will probably add some comments about building the chase. Good luck, John_M
  3. LLigetfa

    LLigetfa Minister of Fire

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    No, there needs to be a firestop at the ceiling. I assume you want to chase in only the attic section to keep in some heat and not run the chase up through the roof. You could simply run a metal radiation shield the length of the attic and call it done or you can frame out the chase and sheet it. I like to use metal studs to frame it out.
  4. FLINT

    FLINT Feeling the Heat

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    thanks guys.

    The chimney will have to go just down from the very peak of the roof, and I was planning on having the chase extend above the roof, with the main purpose being to 'cover' the steel chimney for aesthetic purposes, but also for support. I want to get 15' total flu length to assure a decent draft, and to do that, I have to extend the chimney at least 6' above the roof level. If I go over 5' above the roof, it would require additional support bracing anyways, so I figured, why not just build a chase around it, which would probably help give it support and protection, and would also look better than a big 6' metal tube coming out of my roof. My roof is pretty flat, so only 4' of chimney will be in the attic space. I'm wondering how extensive the chase should be. Can it simply be a 2x4 frame anchored good into the rafters, which I then cover with siding? should it be insulated? If I run the chase above the roof level, I will not need the steel roof flange thing correct? I could just anchor the chimney to the chase - probably at least at the top with some kind of bracket - kind of like how stainless steel chimney liners are supported at the top - except that I believe the class A chimney is also supported by a bracket tied into the rafters just above the ceiling.
  5. John_M

    John_M Minister of Fire

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    flint, I would suggest you start with a Metalbestos chimney support box through your ceiling. This will provide a number of advantages: 1) It will support the weight of the chimney; 2) It will provide the necessary clearances; 3) It will provide a fire stop at the ceiling; 4) It provides a common connection point for the stovepipe to the chimney.

    I would suggest some kind of Metalbestos adjustable stand-off or roof support in the attic near the roof to provide stability to the chimney. Look here: http://www.selkirkcorp.com/Metalbest/Product.aspx?id=208#

    If you go to the link, look to the upper right on the Selkirk site and click on "View Documents" then on "Buyer's Guide" . This will give you lots of info, including some diagrams of what is needed for proper installation. Installing the chimney and stovepipe the Selkirk way is necessary for safety and code compliance.

    A 5' chase above the roof might require some internal (remember the 2" clearance requirements) angle bracing to prevent lateral movement. Would suggest you screw the chase to the support structure you must build to anchor the chase to the roof. The best thing to do is to get someone whom you trust and who is familiar with framing procedures to describe what is necessary in your situation. Good luck, John_M
  6. FLINT

    FLINT Feeling the Heat

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    Yes, I'll definitely go with the support box. Also yes, I was thinking that I would need to start the framing for the chase down in the attic and tie the vertical pieces in to both the bottom and top pieces of the rafters.

    So, If I had some 10' 2x4s that I tied in to the rafters, 4' of them would be in the attic and nailed to the tops and bottoms of the rafters, and then 6' of them would extend above the roof and provide the basic framework for the chase, which I would then tie together with additional 2x4s and then some type of siding.

    aesthetics aside, I don't think I can extend the stainless chimney 6' above my roof without a chase - I just looked at the website with the installation guide, and it said for ever 5' above the roof you have to use a brace kit - except that it looks like the brace kit has to anchor the chimney to the portion of the roof extending UP from the chimney, but I will not have any roof left extending up from my chimney - my chimney will be totally above my roof level, as I have a very flat roof, and my chimney will be almost at the very top.

    let me know if you think its possible or preferable to do this without a chase as I could get over the aesthetics, and if there isn't any functional benefit or necessity of having a chase I could consider not, as it would certainly be easier to not build one.

    Thanks!
  7. John_M

    John_M Minister of Fire

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    flint, I would actually have to see your house with ceiling, trusses, rafters, etc., before I would give you more direction. I might give you incorrect or unsafe info without actually knowing the project. However, I can add this: 1) If your chimney goes too far above your roof you will have a devil of a time cleaning it from the roof. Perhaps you can clean the chimney from inside the stove; 2) The approximately minimum 15' of chimney and stovepipe needed for good draft is measured from the top of the chimney (without the cap) to the bottom of the stove's burn chamber; 3) It might be possible with a shallow pitch roof, to brace the chase or chimney to the other slope of the roof unless that would make the brace too long and therefore not rigid enough; 4) The exterior stainless steel surface of the chimney can be painted with proper preparation and the right paint. I do not know if one of the high temp aerosol paints is or is not the the correct product for painting the exposed stainless chimney. I am certain the Metalbestos site has that necessary information.

    The excellent Selkirk Metalbestose line of chimney components is foreign to me so I am unable to help with this part of the installation. It appears you have already seen some of the drawings showing all the parts needed and how they are connected. You must follow the Metalbestos instructions in all these connections. That is required for safety and code compliance.

    You might be best advised to contact a local TRUSTED contractor who installs wood stoves to have him/her do some of the framing and roof work. Good luck, John_M
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