Wood Heater Experts - I Have a Question

Discussion in 'Homesteading Questions' started by Country Lady, Jan 20, 2007.

  1. Country Lady

    Country Lady Well-Known Member Supporter

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    I was up during the night last night and added a couple pieces of firewood to our wood stove (fireplace insert). I had the damper opened all the way for a few minutes to give it a chance to catch up, then closed the damper down some then went back to sleep. Well we were awakened with a noise. We found the facing that covers up the rest of the fireplace, whatever that's called, blown out and some insulation out also. The little pot on top holding water had been knocked off and water was everywhere. My husband checked it out this morning and everything seemed to be ok. It's going now and is fine. So, "Experts", what do you think of this?
     
  2. caberjim

    caberjim Stableboy III

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    When did you last have a good chimney cleaning? All I can think of is a chimney fire. All that heat and pressure has to go somewhere. If it cannot go up and out, it will try to come out the stove.

    Get a good sweep out there to inspect for damage. I would not start another fire until it is checked.
     

  3. Bearfootfarm

    Bearfootfarm Hello, hello....is there anybody in there.....? Supporter

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    Sounds like it "backfired" Sometimes flammable gasses build up, and with the right mix of oxygen they "flash" and ignite, causing a burst of pressure.

    "When you have a rip-roaring woodstove fire going, your chimney is charged with rising superheated exhaust gases, so the air flow through the firebox is considerable. If you cut down the supply of air too abruptly, the fire instantly consumes the available oxygen, creating a powerful vacuum inside the stove. If strong enough, this vacuum can reverse the flow inside the chimney, pulling a "gulp" of air back down the flue into the firebox. When this pocket of air hits the fire, a mini-explosion occurs, and the resulting sudden extreme pressurization inside the firebox forces smoke out through the draft control, door gasketing and other tiny openings that exist in even the most "airtight" woodstoves. This brief period of pressurization is followed immediately by extreme depressurization (because the explosion consumes all the available oxygen in the firebox), and another gulp of air can be pulled down the chimney, causing the process to repeat. We call this "whuffing", due to the accompanying sound of muffled explosions. In extreme cases, these repeated explosions can cause the stove to actually dance around on the hearth!"
    http://www.chimneysweeponline.com/howhuff.htm
     
  4. Country Lady

    Country Lady Well-Known Member Supporter

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    Bearfootfarm, I think you've diagnosed our problem. I'll be more careful from now on about turning the damper down too soon. The chimney was last cleaned March 2006 at the time the fireplace insert was installed.
     
  5. RedneckPete

    RedneckPete Well-Known Member

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    Bearfootfarm got it right. I've had it happen before too.

    I've had it happen when I toss in too much small stuff and a furious fire results. If I damp this down too much, the resulting flammable smoke starts to make it's way up the chimney. Once, I cracked the door of the stove open to throw something else in, and it back flashed as soon as the door cracked open.

    Another time, when I whipped open the front door of my house quickly, the stove chuffed back into the room, letting go a large puff of smoke out of the air intake vent.

    Since I added my second storey, and made my chimney longer, I haven't had any back flashes. They are rather distressing when they happen, but can usually be prevented by letting the really volatile gasses flash off the wood before damping it down, then damping it down in a couple stages on a stove prone to chuffing.

    Pete
     
  6. quietstar

    quietstar Well-Known Member

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    Thanks Bearfoot...Good information for us woodburners and a good site...Glen
     
  7. diane

    diane Well-Known Member

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    I have had that gas explode on me in the wood cookstove if I am not paying attention and damper down too fast after having a big, hot fire for baking. It will rattle the lids and really put out a puff of smoke. :baby04: