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Shorten Horizontal Flue Run?

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by Rob From Wisconsin, Jan 26, 2006.

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  1. Rob From Wisconsin

    Rob From Wisconsin Minister of Fire

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    Finally disecting my stove/flue setup, and looking
    for ways to improve my draft. In the process of my
    evaluation, I noted that my horizontal flue run was
    almost 24". With a little bit of re-engineering, I
    determined that I could take about 6" off of that
    horizontal run, putting it under 18".
    Is this worth my time? Will I see that much of a
    draft improvement?? Possibly a 25% increase in draft,
    or would it be non-linear? Anyone with any personal
    experience on doing this??

    Rob

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  2. MountainStoveGuy

    MountainStoveGuy New Member

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    You can also put some double wall black pipe in the place of the single wall, and you wont loose as much heat out of that elbow. And of course you can always put another section of class A on the outside to get your stack a little taller and improve draft.
  3. elkimmeg

    elkimmeg Guest

  4. Rob From Wisconsin

    Rob From Wisconsin Minister of Fire

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    Thanks for the advice, but I'm already using Double Wall Stove Pipe.
    Adding more chimney is expensive & may require additional support.
    I'm looking for the biggest bang for my buck.
    Also looking at the rule of 1' horiz. = loss of 5 to 10' vert.

    Rob
  5. pmac

    pmac Member

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    Is there space to replace the two 90 deg bends with two 45 degree bends, to turn the horizontal run into a sloped one? When I had an old coal stove replaced with a wood stove, the installer redid the stovepipe and eliminated a 2 foot horizontal run by using 45 degree bends...
  6. Rob From Wisconsin

    Rob From Wisconsin Minister of Fire

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    No, unfortunately not - going through a basement cement wall.

    Rob
  7. Rob From Wisconsin

    Rob From Wisconsin Minister of Fire

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    So if I understand you correctly, I can "slant" my horizontal run of stove pipe by
    a 1/4" per foot of horiz. run?? If so, I can see where this could somewhat help
    my draft. How much, I would be interested to see...Thanks!!

    Rob
  8. MountainStoveGuy

    MountainStoveGuy New Member

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    check the shops around town that sell your brand of chimney, alot of times pieces come in freight damaged (dinged on the outside) and they might sell you a piece 1/2 of retail or give it to you, we get credit from the manufactures anyway. (at least i do) . At my shop i give it to needy people. If your using simpson duravent, i will ship you one next time i get one if you pay the ups of course.
    A little extra support is not hard. Nothing that cant be acclompished with a little holy iron and conduit. Cheap Cheap Cheap.
    RYan
  9. elkimmeg

    elkimmeg Guest

    Gone fishing
  10. elkimmeg

    elkimmeg Guest

    gone ice fishing
  11. ChrisN

    ChrisN Feeling the Heat

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    Elk, The force you are talking about, the coriolis effect, is real, but it only measurably effects the rotation of very large bodies, ie Oceans, weather systems. The swirling you see in your sink or tooilet is strictly due to the design of the container. It is also a myth that toilets swirl in opposite direstions in north/south hemisphere. I'm not saying the smoke doesn't swirl up a chimney, but it isn't caused by the coriolis effect.
  12. Todd

    Todd Minister of Fire

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    Rob,

    I cut off 6" of horizontal run last year and didn't notice any difference in my draft, but my draft was good to begin with. I cut the pipe so I could move the stove back on the hearth for more room to sit on. I guess it couldn't hurt. The straighter the better.
  13. elkimmeg

    elkimmeg Guest

    gone fishing
  14. webbie

    webbie Seasoned Moderator Staff Member

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    I too have assumed from many years of reading and observing that smoke travels up a round flue in a circular direction - I suppose in the real world it is something quite messier than that, some might go up straight thru the center while other does a dance around the inside, etc.

    But if I am not wrong, this theory has been verified by scientists within our and other industries. It will be relatively simple to confirm this, as I think we have some thermodynamic engineers here...and, if not, I can talk to some of the rocket scientists I know at the test labs, etc.

    Of couse, someone here can build a glass chimney and then give it a go and videotape it!
  15. webbie

    webbie Seasoned Moderator Staff Member

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    Well, that seems a lot different or simply better of an explanation......So you agree that in theory they should spiral, and probably do to some extend, but are messed up (as I mentioned) by a number of factors. I think we can agree on this as the everyday truth, as it has been confirmed by one of the top experts on chimneys, Mr. John Gulland. Here is what he had to say:

    --------------------
    As I learned over twenty years ago by hanging out with the
    slightly looney Phd aerodynamicist in the research division
    of Canada Mortgage and Housing Corp., everything to do with
    air pressures and flows is complicated and messy, so I'm not
    sure there is a simple yes or no answer to that question. I
    suspect what you have is a ragged, swirling mixture rising
    in the chimney, with lots of eddys and currents, and that
    whether those eddys and currents get organized into a swirl
    all in one direction has to do with the surface
    characteristics of the flue.

    The behavior of a plume of hot gas rising, for example, from
    a well-built bonfire in perfectly still air doesn't suggest
    to me that there is a normally present force that tends to
    organize the plume into a 'unidirectional swirl' (if I may
    put it that way). As I recall it sometimes swirls and
    sometimes doesn't, but it is always fairly random and messy.
    I don't know of a technical paper that weighs in on the
    question of swirl or not in a flue. I have certainly heard
    sweeps and other non-scientific experts confidently express
    the view that a plume rises in a swirl inside the chimney,
    but I never took the issue seriously enough to investigate
    it thoroughly.

    If I had to guess, I'd guess it is a crapshoot whether the
    plume swirls in one direction or not.
    ------------------------------------------------------------


    So, again, it appears that is sometimes swirls and sometimes not. It may swirl in one direction......as John said, it's a crapshoot - a gamble.....

    We sure aren't going to solve it here, although I would say that it is not wrong to assume that smoke swirls within a round chimney although not always in an organized fashion.

    I would also suggest that insults and such things have only to do with the swirling of egos, and nothing to do with the subject at hand.
  16. webbie

    webbie Seasoned Moderator Staff Member

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    This one is not a myth. Square flues exist only because these tile can easily stack in the brickyard and also easily be built with square brick and block. This is why you will never see a square pre-manufactured chimney.

    Even in the matter of air ducting, the rectangular ducts are to save basement and other headroom, as you can easily see when you look at large HVAC projects - the ducts are all round.....

    It is very well known by the modern crop of masons (I am writing from the chimney sweep trade show now, where many of them are in training) that round flues are the way to go for better operation. In Europe you will notice many, if not most chimneys with round flues. Premade units such as Isokern all use round flues as do poured reliners.

    So, assuming this is the subject actually being discussed, round is better than square in the subject of flues and stovepipes. Of course, round is also of greater strength.

    craig
  17. Rob From Wisconsin

    Rob From Wisconsin Minister of Fire

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    Thanks for the offer, by my chimney is Excel brand, although I use Simpson Duravent
    for my upstairs stove - works great & drafts like a bandit, and very reasonably priced.
    I will use it in the future when we move & build our next house.
    Thanks again....

    Rob
  18. webbie

    webbie Seasoned Moderator Staff Member

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    Dylan, your wording is very close to correct except that you say in reality they don't and there is no noticeable spiraling. I have personally witnessed spiraling both in chimneys and in as simple as the smoke coming up off a cigarette. So I accept John Gullands answer as the most accurate - that is a crapshoot - a gamble, a sometimes, a possibility - not that it does or does not happen.

    BUT, keep in mind that virtually all EPA an lab testings are bases on this "PERFECT" theory, such as certain chimney draft, certain wood, perfect lab, etc. -

    So, in summary I would say that the collective bunch of us needs to look at our smoke for awhile and see what's up! I should have asked the vacu-stak guys at the convention I just attended....one of them worked on the manhattan project and nuclear subs....and now chimneys for 34 years - maybe he knows!

    Hey, if we can make certain that the liner flex makers have their ridges the correct way for the part of the earth we live on, maybe the spiral pipe can help instead of hurt - I can see it now - NEW RIFLED CHIMNEYS.......get's that smoke out quickly and accurately.

    Elk, I'm waiting for a physicist to weigh in on that toilet effect thing. Only place I ever saw that was on the Simpsons and although the show is sometimes accurate, I would not want to use it for codes.

    "The direction of rotation in draining sinks and toilets is NOT determined by the rotation of the Earth, but by rotation that was introduced earlier when it was being filled or subsequently being disturbed (say by washing). The rotation of the Earth does influence the direction of rotation of large weather systems and large vortices in the oceans, for these are very long-lived phenomena and so allow the very weak Coriolis force to produce a significant effect, with time."

    It is a myth that water spins in different directions on each side of the equator....however, it is truthful that when we have summer here, they have winter and so on..... :coolgrin:
  19. zogboy

    zogboy New Member

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    not p/c not p/c not p/c

    Hardly pc but true and funny, so take it that way.
    I was talking with my granddaughter the other day about Internet chat rooms and forums. We both agreed that it is frustrating to be seeking information and have alleged informed posters reply and turn a simply question into a pissing match.
    That is when she said, “winning an argument on the Internet is like winning a gold metal in the Special Olympics. You won so what: your still a retard.”

    not p/c not p/c not p/c
  20. MountainStoveGuy

    MountainStoveGuy New Member

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    Thats a terrible joke.
  21. Corie

    Corie Minister of Fire

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    How much money are we talking?


    It's pretty common knowledge that laminar flow in square or rectangular tubes experiences more pressure loss than that in round pipes. But you probably won't take my word for it.

    So,

    Courtesy of:

    Impact of Wall Effects on Flue Gas Velocities in Rectangular Ducts and Recommended Revisions to EPA Reference Method 2H

    Stephen K. Norfleet & Robert E. Barton, RMB Consulting & Research, Inc.
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