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Basic Chimney questions

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by bobm, Sep 22, 2006.

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  1. bobm

    bobm New Member

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    Hi All,

    I am ready to purchase a new free standing stove for my family room. I am looking at the Jotul 500 but my questions are on the chimney. I have a new exterior chimney with 13x13 flue titles. The chimney is massive and there is plenty of room around the flue going up the center.

    1) Should I use an insulated stove pipe up this chimney?

    2) Why do I see so many recommendation for a chimney liners. Isn't the best approach to run stove pipe all the way to the top? In this case, why would a chimney liner be needed.

    Thanks Bob

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  2. wg_bent

    wg_bent Minister of Fire

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    A wood stove chimney should be capable of dealing with 2100 degree temps. Stove pipe is not capable of that.

    You should look in the owners manual (on line if you don't have the stove yet) to see what they say.
  3. bobm

    bobm New Member

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    >A wood stove chimney should be capable of dealing with 2100 degree temps. Stove pipe is not capable of that. <
    Ok I think I had my terms confused and I was calling a chimney liner a stove pipe. Would I want to put an insulated chimney liner inside of my clay flue tile?

    Question on general chimney construction, my chimney is a straight shot and when the mason was installing the flue tiles he would just stack one on top of the other and work himself up to the top. Now many chimneys have an offset, how would you handle an offset with a 2' clay tile and keep it air tight?

    Why not build chimneys from the start with stainless liners and skip the clay tiles all together?

    Thanks Bob
  4. BrotherBart

    BrotherBart Hearth.com LLC Mid-Atlantic Division Staff Member

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    The experts will be along shortly, but I would have to believe clay tile is still the norm for two reasons:

    1. For fireplaces, which is what that chimney is really built onto the house for, clay tile is a time tested and proven chimney lining material. Take care of those things and they will last a hundred years. Stainless flex liners like we use for stoves have only been around twenty years or so and are still in the "time testing" stage.

    2. Cost. Imagine what it would cost to stack sections of stainless steel large enough to handle fireplace duty, and weld each section. I would imagine that not just every shade tree welder can do stainless right.

    Stainless steel liners are at best a workaround. Working around the fact that 1. A lot of clay liners are in bad shape and hard to fully replace and 2. Fireplace chimneys are just too darn big to vent a wood stove into.

    If I had found this house ten days earlier in construction it would have ended up with two eight inch round clay flues for stoves instead of two 12 X 8 clay flues for fireplaces. In fact the 12 X 8 clay flue for the eight inch thimble into the basement makes no sense at all. For anything. That is why it now has a stainless liner in it.
  5. bobm

    bobm New Member

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    >The experts will be along shortly, but I would have to believe clay tile is still the norm for two reasons: <
    You sound like an expert to me and I picked up a lot from your reply.

    I noticed from the online sources that there does not seem to be an insulated Chimney liner. What you do is either warp the liner with insulation or pour insulation around the liner during the install.
    Two questions:
    Why don’t they manufacture an insulated liner? Seems to me they could do a better job then wrapping and taping in the field?

    Is class A basically and insulated liner and why can’t that be installed inside a clay flue?

    Thanks Bob
  6. Shane

    Shane Minister of Fire

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    Class A is chimney. typically it won't fit inside a flue. You can use Simpson Duravent Double wall stainless liner.
  7. begreen

    begreen Mooderator Staff Member

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    With 13 x 13 tiles and a stove that takes 6" pipe, I would think class A, 6" DuraVent would fit easily in a 13 x 13 flue if it's straight. It's only 8" in diameter. Seems to me the main question would be supporting its weight at the bottom.
  8. bobm

    bobm New Member

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    Thanks guys, I took a look at the Duravent website and they have an insulated liner for inserts that looks like it will be perfect for my application. I have been talking with a few installers and it’s great to be armed with info.

    One of the reasons I want an insulated liner is this is an external chimney and I would like to improve draft. The 2nd reason is I am not sure that the chimney was built to code. I can only blame my self since I helped the mason build the chimney. Question on Chimney code, if you look at the side view of my chimney you will have external plywood of the framed wall, 3.5” brick, 6” air space and finally the 13x13 flue. I believe you need at least 4” brick against the plywood. Does there need to be an air space between the plywood and the brick? Curious how this is suppose to be done properly.

    One final question, as mentioned above, liners for wood stoves must meet 2100 degree burn for some period of time, but this does not apply to stove pipe. If you have stove pipe connecting the stove to the liner, isn’t it possible that a chimney fire could break out in the pipe which would also be a safety issue. I must be missing something. Bob
  9. MountainStoveGuy

    MountainStoveGuy Minister of Fire

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    You cant use double wall class a inside of a mansonry chimney. it will condinsate between the layers and corrode. You need single wall with or without insulation. As shane mentioned, dura liner from simpson. Homesaver from copperfield, something like that.
  10. elkimmeg

    elkimmeg Guest

    They do it is called Class A
    Many people want the look of a traditional masonry stone/ brick fireplace It infact adds value to the home

    The remenber you are buliding with square or rectangular units bricks and blocks. The size of the liner basically equals 1/10 the fire place opening For example 30" /30" + 900 sq inches the flue liner wound have to have a crossection are of 90 sq inches or more
    A common 12/12 interior cross-sectional area is around 96 to 100 sq in so that would be requires Even though also requires would be 12" rouns ss HT 2100 liner. Have you ever tried to attach a round ss liner to t and form the throat area to it. Don't have to answer that question the answer takes incrediable creativity Beyond most mason's abilities. That why ss liners are not used..

    BB had it right liners are replacement s=ubstutes for failed liners or for correct cross-sectional area of the flue collar of the appliance


    a 2/4 does not measure 2"/ 4" so by the same token a brick is not a full 4" but considered 4" Code has changed it was poorly worded concerning clearance to combustiable with sheatyhing on exterior walls today it allowed for combustiable siding or plywood to touch the bricks. Air space wise code only require 1" surounding the flue if you have 6" ther is no penatlty for exceeding code requirements just an extra margine of safety.
  11. bobm

    bobm New Member

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    >They do it is called Class A Many people want the look of a traditional masonry stone/ brick fireplace It infact adds value to the home <

    Exactly, I started originally in my family room with a large firebox area to house the wood stove. I did not want to take any floor space in the family room so we jut-out from the wall, 4’x5’x3’ wxhxd. This was never intended for open fire thus there is no damper or smoke shelf. We were going to run Class A up the back of the house but didn’t like the look. I supplied the labor on this project and working with the mason we built a chimney up the back of the house. We added the flue in the middle just because I wanted to see how you would do one but I am glad we did. I am still curious how you would add flue tile when your chimney is not a straight shot like mine. Flue title does not bend too easy. I assume flue title does not extend down into the throat area like you said. That begs the question, how is the throat area protected without flue title?

    >BB had it right liners are replacement s=ubstutes for failed liners or for correct cross-sectional area of the flue collar of the appliance <
    My flue is too big for the appliance so I will need a liner. Should I go with an insulated chimney liner for better draft?

    >Air space wise code only require 1” surounding the flue if you have 6” ther is no penatlty for exceeding code requirements just an extra margine of safety. <
    Wow only one inch between flue and wall. This shows you how important the flue is to the safety of the chimney. These section are stacked on top of each other without interlocking just the cement. You can see why there is failures or small undetected gaps. Thanks Bob
  12. elkimmeg

    elkimmeg Guest

    Correct throats must can be formed and poured with 10" of concrete or use flue liners and backed by 8" of solid masonry uints of concrete. Most masons stucko or parge this area with a thin layer of smooth concrete and form it to receive and support the first tile flue. It requires a smooth transition. Your best solution is to install a code compliant insulaterd liner. plus a metal block off at the bottom and top of the chimney run. Especially with an outside chinmney. Don't get talked out of the bottom plating off. Again you asked good questions.

    Finally creative off sets in the flue liners require angle cut joints it can be done
  13. bobm

    bobm New Member

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    >Finally creative off sets in the flue liners require angle cut joints it can be done <

    Ah now I get it. yes that would work.

    >Your best solution is to install a code compliant insulaterd liner. plus a metal block off at the bottom and top of the chimney run.<
    I can understand the bottom block off but what diference would a top block off make? Does that keep cold air from falling down around the outside of the liner? Is top and bottom cut off in the national fire code?

    Thanks bob
  14. elkimmeg

    elkimmeg Guest

    The top plate has many functions. It keeps the weather and natures elements out. It helps prevent cold draft decending down the chimney and it helps support the liner
    The bottom plate is a margine of safety should you develope a chimney fire. It helps contain it and prevents blowback or flashbacks into your living space. IT also prevents the escaping room air from drawing heat out and then cooling the liner, which effects draft and cresote build up. The ideal situation is both atop and bottom block offs creating a dead air space in the cavity. Dead air space prevents drafts and is a form of insulation The warmer you keep that flue liner the better it will draft and the less cresote formation.

    Finally yes there are code that govern the entire installation including plating.

    I think this is my fourth year on this forum I have answered this question many times. I would not install a stove without the backoff plate. I wii not approve an installation without one. Call it the elkimmeg code if you wish,, but I can dig up enough code support language to require it
  15. bobm

    bobm New Member

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    Elk,

    I had my stove installed yesterday. We wrapped insulation around the 6" SS liner. Homesaver has a nice kit which included everything. We inserted the insulated liner into my existing 13x13 flue and sealed at the top and bottom with a plate.

    Curious, does wrapping the 6" SS liner make the liner 0 clearnce? My chimeny has lots of space around the flue title at the bottom, so above the bottom plate on the outside of the flue tile we installed FG insulation. Sweep said this was fine. I wanted the instulation so the bottom plate would refelect the heat of the stove back down and out into the room. Is this ok?

    Bob
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