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Discussion Forum

flue downdrafts

boag1 | Posted in Energy, Heating & Insulation on January 30, 2003 05:27am

I have a number of chimneys in my house, and they are tall. When the temperature starts to warm up outside, say in the high 40’s the chimneys develop a good downdraft. In spring the the outside temp can be extremely pleasant, but inside it is COLD. If we have built a fire within the last few weeks the downstairs smells of smoke.

I closed the flues and have a decorative cover over the front. The downward force is too powerful for these to stop it. I’ve heard of a pneumatic bladder that be inserted in the fireplace, have seen one just heard of them.

Any suggestions. 

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Replies

  1. friendlyguy | Jan 30, 2003 09:10pm | #1

    I've burned wood all my life, Dave, and installed many types of wood burning stoves in different types of houses, and climates. The factors affecting draft that you've mentioned, outside temperature and chimney height are among the most important, to be sure.

    A few others are surrounding topography, adjacent structures and trees, prevailing winds, and flue design. Suffice to say, heat does rise, but smoke/creosote odour can be blown back down the flue if any of these factors apply. You'll need to do a really thorough analysis of your site, as well as the distance of your chimney from structures that could be deflecting prevailing winds in order to understand when those wrong conditions are occuring. There are standards for obvious distances of chminey height relative to proximity to a nearby ridge, for example. On the positive side, this problem does not need mitigation by installing a plug in the flue, but is completely solvable, if the real problem is correctly identified. Most chimneys do work well. Enjoy the day, h. 

    1. boag1 | Jan 31, 2003 05:23am | #3

      Appreciate the input. The configuration of the house and surrounding area doesn't provide obstructions. The house is three stories with a basement. The chimney extend above the house an adequate distance. I built the house myself and it is tight. Good windows, no drafts, wrapped. and caulked. Total chimney height is probably 35- 40'.

      The chimneys are masonry and retain the cold, the problem occurs with (for lack of a better term) a temperature inversion between warm outside and cold masonry. This is why I was considering a liner plug. Something positive to stop downward air movement.

      1. User avater
        rjw | Jan 31, 2003 05:48am | #4

        Perhaps one of those top of the chimney, chain operated dampers in the chimneys?

        I don't know how well they actually seal, but the ones I see look pretty tight.

        What kind of heat and hot water do you have?  If combustion based (nat gas, oil) you should probably have the draft on the furnace/boiler flues checked for backdrafting as well.

        _______________________

        "I may have said the same thing before... But my explanation, I am sure, will always be different."  Oscar Wilde

        1. coolcall | Jan 31, 2003 08:50am | #5

          Bob,

          can you point me towards a source of the elusive "top of the chimney, chain operated dampers" been stuck with the competence of the local big boxes and thought about building my own but if someone is making one for less than an arm and a leg well hey.....

          in advance thanks

          1. UncleDunc | Jan 31, 2003 09:30am | #6

            Go to http://www.google.com and try this search string.

            chimney top damper (chain OR cable)

  2. MartinHolladay | Jan 30, 2003 09:18pm | #2

    Dave,

    It is most likely that air is entering your house through your chimney because your house is under negative pressure.  There are many possible causes of this;  if the house is relatively tight, it can be caused by operation of exhaust appliances, including bath exhaust fans, kitchen range hood fans, clothes dryers, central vacuum cleaners, or combustion appliances (furnace, boiler, or water heater).  If you have a big hole connecting your second floor to the attic (happens all the time -- bad attic access hatch, an unsealed chase, etc), then indoor air may be leaving your home continuously into the attic, creating negative pressure.  Your fireplace flue is simply the easiest route for makeup air.  Get your house inspected by a weatherization expert capable of diagnosing pressure imbalances.

  3. DavidThomas | Jan 31, 2003 11:36am | #7

    Do all the chimneys deliver cold air under those conditions? Maybe not. The cold ones are easy to spot. The ones that are sucking up warm air aren't so noticeable. But some could be discharging warm air up while others are replacing that air with cold, outside air. In a tight house, the warm air has to be going somewhere for all the cold air to come in. And a chimney (or another type of flue) is an obvious route.

    Duct tape some visqueen across the fireplace openings. The amount of deflection in or out should give you a qualitative sense of the vacuum or pressure (loss of warm air or introduction of cold air), respectively.

    David Thomas   Overlooking Cook Inlet in Kenai, Alaska
    1. User avater
      CloudHidden | Feb 01, 2003 07:39am | #13

      I wanna second your thoughts. We thought smoke was getting out of the one fireplace because it was two-sided with a large opening. Just recently wandered into the other room when a fire was going and saw smoke coming down through that one where the damper fit poorly because of excessive mortar. Got the damper to close properly, and no more smoke from fires. Air takes the path of least resistance, and he could easily have the air cycling out one and in another.

      1. boag1 | Feb 01, 2003 05:11pm | #14

        In my situation we have no vented appliances, no power vented bathrooms, etc., the chimneys are dedicated to the fireplace, and this problem is extremely apparent in early spring when the heater is off and the windows are still closed. When it is say 60 deg outside it's like standing at the mouth of a cave with the cold air coming down.

        I have also experienced the problem mentioned above where two stacks are side by side. With a fire in one fireplace the other fireplace sucks down the smoke and fills the other room with smoke. To solve that problem we put a small camping stove in the fireplace to cause an updraft.

        Also the dampers are tight, and tight as you can get with metal to metal.

        1. MartinHolladay | Feb 02, 2003 12:08am | #15

          Dave,

          Have you checked your attic for air leaks (bypasses, unsealed chases, etc.) that might be turning your entire house into a competing chimney?

          1. boag1 | Feb 02, 2003 04:29am | #16

            I haven't preformed a rigid test, but the attic access is up three floors and behind two door, which are closed. The access itself is a 16x24 access insulated and latched, in the ceiling. Considering the total volume of the house relatively small, however, none the less I would consider it sealed tight.

          2. User avater
            rjw | Feb 02, 2003 08:03am | #17

            You won't know if it's sealed tight unless you look, mistakes are often made, and there is a built in chase around the chimney itself if built recently that needs to be sealed.

            _______________________

            "I may have said the same thing before... But my explanation, I am sure, will always be different."  Oscar Wilde

  4. junkhound | Jan 31, 2003 05:02pm | #8

    "pneumatic bladder that be inserted in the fireplace"

    stick a cheap plastic beach ball in the flue and inflate it - used to do that trick to seal ducting temporarily

    1. boag1 | Jan 31, 2003 10:47pm | #9

      A lot of good discussion.

      I thought of something like a beachball, however I felt that the ball was too rigid in shape and wouldn't conform to irregularities of the smoke chamber. Looked for something on the order of pliability of an innertube, but linear.

      1. RodBishop | Feb 01, 2003 02:12am | #10

        Here Dave, try this page,  it's about the Lyemance Chimney Top damper         Rod

        File format
  5. Piffin | Feb 01, 2003 04:28am | #11

    My bet is on pressure imbalance from other combusters and vented appliances.

    If that is the case and you plug the chimney with a bladder, your house will still have a defect that needs correction to be healthy.

    .

    Excellence is its own reward!

    1. User avater
      rjw | Feb 01, 2003 05:45am | #12

      My bet is on pressure imbalance from other combusters and vented appliances.

      I was thinking that - the tallest chimney is going to make lower chimenys air intakes!  But I wonder about the timing, and it only happening in certain weather conditions.

      Whadda ya think?_______________________

      "I may have said the same thing before... But my explanation, I am sure, will always be different."  Oscar Wilde

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