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Translating flue surface temps to internal temps?

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by jtcedinburgh, Nov 29, 2006.

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  1. jtcedinburgh

    jtcedinburgh New Member

    Joined:
    Sep 19, 2006
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    Loc:
    Fife Riviera, Scotland
    Just wondered if there exists a 'rule of thumb' to allow me to guage the internal temperature of my flue-pipe based upon the external thermometer reading. Obviously roughly rather than precisely. Single wall pipe.

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  2. BrotherBart

    BrotherBart Hearth.com LLC Mid-Atlantic Division Staff Member

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    Nov 18, 2005
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    Loc:
    Northern Virginia
    It is generally figured to be half of what the actual internal flue gas temp is at the moment. That is born out by my observations with a probe and a surface unit on the same pipe.
  3. begreen

    begreen Mooderator Staff Member

    Joined:
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    Loc:
    South Puget Sound, WA
    This may vary quite a bit with the stove? I've had the flue thermometer in since Saturday. It's taught me a lot and changed my burning habits. At first I was getting rough parity between the flue temp (double-wall) and the stove top. I would get the fire going good, close the stack damper then run the stove at about the half-way point for the air control. Visually I'd be getting a nice blaze and saw stove top temps and stack temps roughly equal at about 550-600 peak.

    However, I found that if I choked the air control down, (1/8 to 1/4 open depending on the wood), right as the wood is at it's maximum gasification point, that I could keep the stack temp from exceeding 450 while the stove top could be up to 650. Quite a difference. The stove was burning on almost pure secondaries. Since then I've been burning 24/7 and the stack has not gone over 400. Average peak top temp has been 550-600. This has helped reduce wood consumption without compromising heat output. I love learning something new and really like having two thermometers now.

    What's interesting is that in spite of what the manual says, the air control does not really reduce stove temps during this phase of reducing the fresh wood to coals. With doug fir I have to close it all the way down and it still burns with a roar and rumble. The only real control during this phase is add less wood. In a couple hours, once the stove is burning pure coals, the air control must be opened up about halfway to maintain about 400 stove top temp, 300 flue temp.
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