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Wood Furnace Flue Questions

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by Catfish Cleatus, Feb 23, 2013.

  1. Catfish Cleatus

    Catfish Cleatus New Member

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    I have a double flue chimney. One flue for the fireplace on the first floor. The other flue runs to the basement and has the hotwater heater connected and a filled in port just below that where the old natural gas furnace used to vent. That is now filled in with what appears to be cement. Both holes in the basement flue I believe measure to 6in. Would I be able to remove the current hot water heater from this flue and use this basement flue for a wood furnace or stove?

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  2. biggkidd

    biggkidd New Member

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    How many flues come out of the chimney? Are they round , square, or? Is the liner clay? Need more info to get a correct answer.
    Larry
    Sorry missed double flue. Are they clay? What size how tall?
  3. Catfish Cleatus

    Catfish Cleatus New Member

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    Just bought the house a few months ago and haven't been up there to look down as of yet. That is something I need to do and get them inspected this spring. Double flue. I just looked up the fireplace flue and it is big and rectangulare maybe square after the fireplace brick. The fireplace one appears around a foot in diameter and clay.

    As for the second flue that goes into the basement and only the hot water heater is using at this time I'm not sure until I get up there and look down. Given that the basement flue once vented the hot water heater and a gas furnace.... I'm not much of an expert but can I assume that it is also at least a 6 inch square clay... maybe 8? This is the one I may look at pulling the water heater off of and putting an add on Kuuma wood furnace. House was built in 1970 and I'm pretty sure the chimney was original with the build. Thanks!
  4. biggkidd

    biggkidd New Member

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    Lets hope the experts chime in. But my thinking is youll need to add another insulated liner inside what you have. To my understanding you need a good strong draft which comes from heat rising up the chimney. Think of the flue as a vacume pulling air through the fire. Hope to hear from others.
    Larry
  5. STIHLY DAN

    STIHLY DAN Feeling the Heat

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    You will need to install a 6 in liner in the flue. No worries tho, pretty cheap and not that hard to do.
  6. Catfish Cleatus

    Catfish Cleatus New Member

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    I went up there and meausred it out. The flue that I would be interested in venting a wood burning furnace to is clay lined 7x7 square inches inside dimensions. Some pieces of morter between the sections of clay liner stick out a bit on the way down. A slight turn maybe 20-30 degrees. Can I fit a flex 6in flu liner insulated or uninsulated down this? Or is it just fine to hook up the furnace to it without the liner? Is a clay lined flue considered a class A chimney?
  7. maple1

    maple1 Minister of Fire

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    So you have an oil fire water heater now? Or gas? Or ?

    And you plan on maybe replacing it with electric?

    Replacing an oil one with an electric one is a good plan in itself.

    I'm not so sure you'd need a new liner if your existing one is in good shape - you might be good to go. You should maybe have it inspected by a good chimney guy to be sure though. Is it an inside chimney or outside?
    STIHLY DAN likes this.
  8. Catfish Cleatus

    Catfish Cleatus New Member

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    Yes I would get the gas water heater off of the flue. Go tankless and vent it somewhere out the side of the house. As for the flue it is a tad under 7 in. More like 6.75x6.75 inches square clay liner inside with some pieces of mortor hanging out. Probably about 25 ft of flue length with about 15 ft of it running inside the house with a slight bend. Would a gasification wood furnace hook up get me good draft and keep this flue warm enough so as to not build up creosote too fast? Is this flue considered class A? Or do I have to insulate it with a SS liner and would it even fit? Does anyone out there hook up wood stoves, furnaces, or boilers to clay flue liners or is that a thing of the past? Thanks everyone!
  9. STIHLY DAN

    STIHLY DAN Feeling the Heat

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    That should work. Get it inspected, mortor in the clay liner sounds fishy to me. Send LAMPPA an e-mail about the size chimney to be sure. They will get back to you, customer service is top notch there.
  10. laynes69

    laynes69 Minister of Fire

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    You won't get a 6" flex liner down the chimney if needed, they average 6 5/8" or roughly the size of a paint can. A 15' length inside sounds awfully long, is it vertical or horizontal? Is the rest of the 10' the chimney height outside?
  11. Catfish Cleatus

    Catfish Cleatus New Member

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    The flue in question runs out of the basement and through the first floor within an add on. Then goes up the ceiling of that room and outside up the side of the second floor all vertical. A bit of a bend in the fluen only not the chimnney. Probably more like 10' indoors and 15' outdoors for 25' total length.

    I think its probably safe to say I can't jam a 6" SS liner down the 6.75 square clay liner without major dificulty. Is the single wall SS liner about the size of a paint can? If I would try this it would be with a single wall flexible SS liner and then insulate with the chimney insulation mixes that are out there. What does everyone think... worth a try and is it a legal class A liner?
  12. laynes69

    laynes69 Minister of Fire

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    A 6" single wall stainless flex liner is over 6" in diameter. If the chimney is sound with no cracked or missing tiles then I would use it, pending inspection. Otherwise to line the chimney would require removal of the existing liner and replacing it with an insulated flex liner. The current liner should be within the size requirements of the furnace. One of the problems is even though the chimney may look fine, it may not be up to code. That's where a sweep or professional should have a look to be safe.

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