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  1. pete97

    pete97 Member

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    I have an older Kodiak Wood Stove at camp. Here is a picture of it. It uses an 8" pipe. My question is can I run 8" single wall pipe straight up inside the camp and when it reaches the insulated pipe can it be reduced down to 6" insulated pipe that goes through the roof? Thanks Pete

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  2. Cazimere

    Cazimere Member

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    Your stove will draft much better with 8" all the way.
  3. Gamalot

    Gamalot New Member

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    I am posting just to get signed in to this thred and watch for answers from the experts.

    I have always thought that it is OK to run a 6 inch pipe in to an 8 inch but that it is NOT OK to reduce an 8 inch down to 6 inch. Thats my uneducated opinion but I do feel the stove was made with the 8 inch for a reason so the fire box might require the greater draft then a 6 inch will allow.

    I have a beautiful Gold Marc "Monticello" wood/coal stove out in my garage that is for sale because it requires an 8 inch pipe and there is no easy or inexpensive way to increase the 6 inch chimney I now have that I am aware of.

    Gary
  4. wellbuilt home

    wellbuilt home Minister of Fire

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    I guess you could do any thing you want . I don't think it would cause a danger ,but the stove would not have as much draft as it should and wont burn 100% My sister has a vigilant and had a 8" to6" but she had a oval outlet on the stove so i had a metal guy make a part that went from the VC oval to 6 " round The part was about 12" long. I like to clean my flue from inside so i like to run my brush up on straight pipe. We changed the flue to 8" all the way up, the stove burns much better. John
  5. LLigetfa

    LLigetfa Minister of Fire

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    Some people will probably say it isn't to code but we used to do that all the time. We would use two long tapered reducers that gradually reduced 8 to 7 and then 7 to 6. The large 8 inch pipe slows the rise to scavenge more heat through the stove pipe. As it rises and cools, the taper accellerates the flow. If there is a lot of cooling, reducing the size sooner speeds the flow out of the chimney so that it doesn't have as much "hang time" inside the chimney, improving draft.

    The overall amount of flow with the stove door closed is controlled by the air intake. If there is not enough flow to keep the chimney hot enough, there will be diminished draft.

    With the door open of course your chimney draft would be negatively affected by the smallest section but if the chimney is too cool that too will be a negative factor.
  6. pete97

    pete97 Member

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    I installed it in the camp I'm building as I described. It drafted fine and I can leave the doors open with no smoke. The problem I had was that when I cut back on the air for over night the next morning there was creosote running down the pipe on the outside of it. I don't know if the reduction in size caused this. Pete
  7. Backwoods Savage

    Backwoods Savage Minister of Fire

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    Unseasoned wood caused the creosote.
  8. LLigetfa

    LLigetfa Minister of Fire

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    Reducing the size sooner can speed the flow through the chimney, increasing the flue temp but as BWS said, unseasoned wood caused the creosote. If you have to burn less than ideal wood, give it more air to keep the flue temps up. Just because you don't see liquid creosote running down the pipe doesn't mean you don't have it building up in the SS chimney and cap area.
  9. pete97

    pete97 Member

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    Wood was seasoned. It has been 2 yrs since it was cut. It was alittle wet though from snow and rain. Pete
  10. LLigetfa

    LLigetfa Minister of Fire

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    That just goes to show that the word "seasoned" is meaningless as many here have been saying over and over. I've seen two year old wood rot outside because it's so wet.
  11. JerseyWreckDiver

    JerseyWreckDiver New Member

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    Numerous answers to your question, all of equal importance.
    Air supply, combustion, and exhaust are all part of the same balanced process, change one factor and you affect them all.

    There is of course the fact that building & other codes prohibit a flu from being reduced at any point beyond the flu collar and the flu must be equal to or larger than the flu collar of the stove.
    Without failure there are lots of people that love to say "Codes Schmodes, I know what I'm doing" But the other side of that is not just the municipal code inspectors but the insurance companies that will leap at near light speed to any potential opportunity to deny a claim. If your setup is not up to code & manufacturers specifications for installation then any mishap you may have from a fire to Carbon Monoxide poisoning would not be covered. How much could that possibly cost you?
    Then there is the issue of proper function. Your stove was designed and tested to work correctly with an 8" flu. Changing that changes other factors that were not accounted for in the testing that was used to obtain the listed status. As mentioned, reducing the flu will accelerate the draft, which will also accelerate the draw of combustion air through the intakes, which can allow the stove to be overfired well beyond it's design limits. Higher potential maximum temperatures could lead to damage to your stove or a fire. The min. clearance to combustible materials was determined using the draft and max firing rates of an 8" flu. Many people may think "more draft is better", not necessarily... The higher your draft the faster combustion gases are drawn from the stove (combustion chamber) draw them out too quickly and you may be drawing out lots of unburned combustion gases, preventing secondary combustions and actually increasing creosote buildup by running tons of dirty exhaust through your flu... Not to mention all the lost BTU's (cardinal sin...) and excess smoke/pollution. Also, change the amount of air being drawn through the system and you change the combustion air requirements of the structure. Will the building house sufficient combustion air supply for a system that is now running in overdrive? If not it will choke the combustion, cause incomplete burn, create more Carbon Monoxide, more creosote, maybe backdrafting. In short, it's not just a pipe your messing with, it's an entire system with a lot of variables. An engineer was paid a lot of money and took a lot of time to make sure all the variables were going to play nice together and now your going to change one of them....
    Now for as much as this sounds like the sky is falling, you may be able to go years, even decades with no problems at all, but for the potential negative outcomes is it really worth not just replacing the 6 inch flu with the correct 8 inch it was designs to work correctly with and being done with it?
  12. Cazimere

    Cazimere Member

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    QUOTE: Reducing the flu will accelerate the draft, which will also accelerate the draw of combustion air through the intakes, which can allow the stove to be overfired well beyond it's design limits.:QUOTE



    I believe the opposite would be true. Going from 8" to 6" will slow the draft and constrict the draw of fresh air causing poorer
    combustion and heat output.
  13. humpin iron

    humpin iron Feeling the Heat

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    is your pipe upside down?? crimped end up? or crimped end into chimney?? If it was right liquid would not be able to leak out. 50% reduction in volume 6" vs 8". Would probably also help if you stopped turning it down soooo low over night.
  14. LLigetfa

    LLigetfa Minister of Fire

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    Maybe too much money. I work with a lot of engineers and have seen my share of incompetence. That said though, you do raise very valid points but WRT draft, the variables that affect draft cannot all be addressed in the design and some design considerations may be to the lowest common denominator.
  15. pete97

    pete97 Member

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    The crimped end is up so I guess I put it on wrong. This isn't the first stove I installed but the first one that I put the pipe on upside down. Go figure.
  16. LLigetfa

    LLigetfa Minister of Fire

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    No, that is how it was intended. Some people have been known to reverse it but that requires a section with two male ends, one probably hand crimped.
  17. humpin iron

    humpin iron Feeling the Heat

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    Crimped end always points down, toward the stove (on a wood stove). The reason it didn't fit was because stoves of that era commonly used preexisting pipe and simply sliced off rings and welded them to the stove. That pipe was too big to fit over and too small to fit into. You have to hand crimp the snot out of the first piece and get it into the stove.
  18. Gamalot

    Gamalot New Member

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    I always installed the pipe crimp down back in the old Smoke Dragon days before I went to coal. I don't remember having any real trouble or having to hand crimp any sections.

    I do remember having to cut the crimped end off a couple of times to give me a double female section.

    My buddy did his crimp end up once and ended up having to re do it because of the honey drips running down the outside of his pipes and causing a stink in the house as the gunk cooked.

    I seriously doubt these pipes were ever intended to be installed crimp up for wood stove applications!

    Gary
  19. savageactor7

    savageactor7 Minister of Fire

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    ^ yeah while reading through the threads I was coming to the same conclusion. If you're gonna reduce it definitely do it at the stove.
  20. PunKid8888

    PunKid8888 New Member

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    I have been recently running my vigilant min 8inch flue through a 8 to 6 inch reducer, and then into a 6.5 x 6.5 lined chimney. It worked ok but the stove could come up to temp real fast. It was to the point where I felt like I needed to check on it every 20mins. So it is possible but you might end up regretting it for peace of mind.

    I now was able to jam a 7inch pipe through the thimble section (6.5x6.5) so now I am running a 8inch to 7inch reducer. so far I have only had two fires through it both times the stove seamed to draft way better, and the stove seamed to have a more even temp. I imagine that If I went true 8 inch all they way the stove would run even better, but that is just not cost effective. This stove will last me this season till I change over to a true 6" designed stove.

    as for the pipes every instruction sheet I have read online from stove manufactures says for crimped end down so that no possible way of creosote falling out with gravity.

    Any time you reduce dia you increase speed but you have less volume. Simple example is a garden hose. run it open, loads of volume but not much velocity, put your thumb over it and plenty of velocity but I guarantee if you try to fill a bucket it will take longer.

    So reducing diameter should reduce draft, which I think is more volume dependent

    I am a firm believer to each there own, if you want to reduce it to 4inches thats fine just be safe about it and don't expect it to run the same as with a 8inch, and don't think you will get approvals from others.

    Thats my 2 cents
  21. bsruther

    bsruther Minister of Fire

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    I always put the crimped end of the stove pipe pointing up with the female end of the pipe above it fitting down onto it. Look at an 8 to 6 reducer or a 6 to 8 increaser and see which end is crimped.
  22. Gamalot

    Gamalot New Member

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    I won't argue with anyone on this except to say if you point the crimped end up and have creosote dripping down the external side of the stove pipe, you are creating a disaster if you ever have a chimney fire on the out side of the pipe.

    Let comon sense prevail and keep any possibilities of flame on the inside of the pipe!

    Argue all you want but keep the flames contained!

    Gary
  23. JerseyWreckDiver

    JerseyWreckDiver New Member

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    Pick up any introductory level Physics book and look up fluid dynamics or specifically Bernoulli's Principle and you will see that the opposite is not true. Take a rushing stream that is ten feet wide and narrow a section of it down to six feet wide. What happens? The water velocity increases through the restriction...
  24. Peter B.

    Peter B. Feeling the Heat

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    And if you have any reason to doubt the water analogy, every automotive or small engine carburetor ever made utilizes the same principle... with air as the fluid medium. Also known (I believe) as the venturi effect.

    Peter B.

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  25. humpin iron

    humpin iron Feeling the Heat

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    Understand that a stream or an engine are "active" systems with a force being placed upon one side. A stove is a passive system.......kinda like a toll booth that goes from 8 lanes down to 4.
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