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Condensation leaking from boiler and chimney

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by antos_ketcham, Apr 7, 2008.

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  1. antos_ketcham

    antos_ketcham Member

    Joined:
    Mar 5, 2008
    Messages:
    155
    Anyone out there with outdoor installations have trouble with condensation forming and leaking from their furnace and chimney? I don't get a lot, but it sure smells bad and I don't think that back will ever come out of the concrete floor. I guess I am also a little concerned about rusting inside the boiler itself. Thoughts?

    Pete

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  2. Richardin52

    Richardin52 Member

    Joined:
    Mar 28, 2008
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    Loc:
    A farm in Maine
    Could be a couple things.

    The gases going up the chimney have to be hot enough to make it out the chimney before they cool to the point of condinsating. Have you ever seen a chimney built on the outside of a house that was leaking creosote? That's because the smoke that carries any moisture outside is cooling down before it gets to the top of the chimney, remember cold air can't hold as much moisture as warm air. It literally rains in the chimney. So you need chimney gases with enough heat to carry moisture out (normally at least 300 deg. with dry wood) and a chimney that's the right size so the gases don't cool down before they get outside.

    If your burning wood with a lot of moisture in it your smoke will be heavily laden with moisture. If that is happening you will need more heat going up your chimney to carry all that moisture up and out.

    So if you are burning green wood remember you old science class.
    Heat and energy are related. If your burning green wood your boiling water and that takes energy. It takes heat to create energy therefore no mater what some boiler salesmen tells you it takes a lot of heat to boil water. That coupled with the fact that you need more heat to get that moisture out the chimney. It's not hard to see why outside boilers use so much wood.

    I have been burning wood either in a wood stove or a wood boiler for 35 years. After 35 years of working up wood I know that it takes a lot longer to dry unsplit wood than split wood. It also takes longer to dry long wood than short wood. 16" or 20" compared to 4 foot wood.

    If your burning what you think is seasoned 4 foot unsplit wood cut one in half sometime take a wafer say an inch think out of the middle of that log. Then weigh the wafer, write down the weight then split it into little pieces. Take the little pieces, being careful not to loose any, and put them into either a oven set at 120 deg. for 24 hours, or in a microwave set a five minutes. Heat the wood and weigh it, then heat the wood and weigh it. Do this until the weight stops dropping. Now you have dry wood. Now weigh the dry wood. If you know the dry weight of the wood and the weight of the wood before you dried it you can figure out what percent of the wood was water.

    You will see that unsplit 4 foot wood dried for a year it not close to being dry and that’s why boilers that take large chunks of wood will never be efficient. It's just simple science.
  3. antos_ketcham

    antos_ketcham Member

    Joined:
    Mar 5, 2008
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    thanks for that. I am burning reasonably dry wood. Mix of split and unsplit and a mix of hard and soft wood. I am wondering if what I should do is buck what Greenwood says and have an 8" chimney the whole way up rather than going from 8 to 6 as it recommends - that is what mine does. I also have single wall pipe for the first five feet and then it switches to double wall metalbestos. Maybe this is part of the problem. My temp. probe in the chimney doesn't show my flue temps getting above 300 even when the unit is wide open.

    Pete
  4. DKerley

    DKerley New Member

    Joined:
    Jan 27, 2008
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    Loc:
    Yukon, Canada
    Hi Pete,

    It is interesting that your flue gas temps are not very high even though, your heat transfer tubes are probably coated with creosote. I burn extremely dry spruce and pine and have at times (depending on the stage of the burn, temps over 500 deg. This is a result of the creosote build up on my transfer tubes and dry dry wood. I have not had any external leakage of creosote and or moisture from condensation inside the boiler. I have had, condensation inside the boiler on the transfer tubes. I know this a s a result of disassembling the GW and finding a small piece of the insulation stuck to the tubes with rust developing. When operating the GW, have you been able to maintain normal (160 - 180 deg) water in the boiler? I have found out that the main reason for creosote development on the transfer tubes is caused by return water temperatures (from external heat exchanger) being too low ie: less than 135 deg. There is a fix for this. The installer that I use will be installing some boiler protection to prevent the cold water from entering the boiler.
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