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Secondaries and pipe damper

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by johnstra, Feb 12, 2011.

  1. johnstra

    johnstra Feeling the Heat

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    The secondaries go crazy on my stove when I close the pipe damper. I've confirmed that the damper closes. My expectation is that the damper would limit draft and that would cause the secondaries to quiet down, but the opposite appears to happen. Any ideas why? Do secondaries operate independent of chimney draft?

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  2. begreen

    begreen Mooderator Staff Member

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    Sounds like strong draft. By reducing it a bit, the stove is working more as designed. I would guess that with the damper open the flue temps are much hotter.
  3. pen

    pen There are some who call me...mod. Staff Member

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    When you say pipe damper are you talking one of these?

    [​IMG]

    Or are you referring to your stoves primary air control?

    pen
  4. NH_Wood

    NH_Wood Minister of Fire

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    I find the same thing. I think what happens is that the closed damper traps additional smoke in the fire box which ignites by secondary combustion. If I nearly close the damper (normally just to 1/2 closed if I need to use the damper) I can tell that the firebox is filling with more smoke than usual. This is when I will have a wall of secondaries pouring form the top of the glass to the bottom. Cheers!
  5. johnstra

    johnstra Feeling the Heat

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    Yes, Pen, one of those. Mine is subtly different. It has a larger hole in the center of the damper. Simpson makes a DVL adapter w/ damper that goes onto the flue collar - that's what I have. When closed, it still leaves a fairly large gap between the inner wall of the pipe and the edge of damper. I know they are designed not to block the vent entirely.
  6. Jimbob

    Jimbob New Member

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    I'm thinking it's because when the damper is open, air is drawn through the secondary faster, so it doesn't get a chance to heat up before it exits into the top of the firebox. That air has to be hot for the secondaries to work well.
  7. precaud

    precaud Minister of Fire

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    No, not independent on draft. Yes, it shows you how much excess air comes out of the secondaries under normal draft conditions. Reducing the draft slows their velocity, so you see more mixing as the air comes out of the holes.

    You might check your stack to see if it's still burning clean when you see the 2ndaries doing that.
  8. laynes69

    laynes69 Minister of Fire

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    We had too much draft for our furnace to operate properly. I ended up reducing the primary and secondary ports and eliminating our barometric damper and key damper on our 32' chimney. We now have longer, hotter, cleaner burns and are using less wood. I read about the flordia bungalow syndrome and I felt it was our problem. Our furnace was pulling combustion air through it so fast it gave nothing time to combust. I think it was diluting the firebox. Having too much draft can have a negative impact and of course too little also. If your having good luck with the key damper then thats great. I tried the key damper and I couldn't get it right.
  9. johnstra

    johnstra Feeling the Heat

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    This is great information... Thanks!

    My elevation (~4800') is surely a factor too. I wonder how exactly that affects the behavior of the stove. There is less O2 and of course air pressure is lower too. I haven't given much thought to velocities when considering draft through the stove. Could be that my "lighter" air moves too quickly through my stove and that's why the damper helps rather than hinders secondary combustion.

    There's just no end to the fascination :)
  10. DonNC

    DonNC Member

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    What stage is the fire in when you close the damper? Is it roaring?
    I want to try to duplicate this here.
    Is the primary air closed?
    --

    Me thinks Pen likes that picture :coolsmile:

    Just noticed the little spring on the handle is crooked. Glad u posted it because I was thinking my damper was slightly damaged because the spring looks exactly the same
  11. precaud

    precaud Minister of Fire

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    It may not be making any difference in actual secondary combustion - but only changing where in the stove it is happening and making it visually more satisfying. That is why I suggest, you should check your chimney output to see if there is any visible difference.

    Your read on the effects of elevation is basically right. Less air pressure and O2 means that more secondary air is required to burn cleanly at altitude. So I wouldn't go nuts with the damper. If your stove has a cat, this is all less important.
  12. begreen

    begreen Mooderator Staff Member

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    +1, that was the point of my reply. I'd much rather have good secondary combustion inside the mass of the stove than up in the flue.
  13. johnstra

    johnstra Feeling the Heat

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    DonNC - I'm closing the damper after I've closed my primary air all the way and secondary combustion is active. My stove yields max heat output with the primary fully closed. I've been experimenting with the damper to keep even more heat in the stove rather than up the flue.
  14. shawneyboy

    shawneyboy New Member

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    I would like to know what the outcome of your experiments with the damper are. I have one on my Mansfield but do not use it. Please keep us posted.
    Thanks in advance,

    Shawn

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