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  1. #1
    Join Date
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    Default Venting a furnace

    We recently purchased a 60 year old home and upon buying we replaced the old furnace with a Lennox G60UH(x) series 80% efficient, 2-stage gas furnace.

    The old furnace vented out to an OLD mason chimney. When we had the new furnace put it, the furnace guys put in a new liner to the chimney.

    The chimney is in major disrepair and needs to be replaced. We would like to know if we can replace it with "something else" and if so, what are our options for "something else?" We've heard that PVC can be used, but perhaps not on an 80% furnace.

    What options do we have? If we can go cheaper by just tearing down the already-crumbling masonry and adding on a pipe - great!

  2. #2
    Join Date
    Feb 2008
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    554

    Default Re: Venting a furnace

    GF08:

    It's unlikely you would be able to use PVC as a vent as the exhaust of an 80% AFUE furnace is perhaps around 300 degrees or better--you will have to check out the specs on the furnace to verify the exhaust temp.

    Ordinarily, a Type "B" stainless steel or galvanized double-walled vent is installed thru the roof & the deteriorated masonry chimney is left in place until the roof is ready for a new shingle job---it is then removed, at least to below the roof surface & the new roof installed.

    This would of course depend on the level of deterioration of the chimney---if it is to the point where it is letting in rain, or is structurally unsound, then it would have to be removed---this would leave a hole in the roof that can be easily sheathed over with wood, but a "sore spot" would have to be covered over with shingles that would be very hard to match in regards to color & texture with those already on the roof.

    Depending on the size of the existing chimney, there are brick look-alike chimney housings that can be installed as a possible option.

    It would perhaps be best to get several local estimates from furnace installers and chimney installers to get a full idea of your options.

    http://www.duravent.com/docs/instruct/L204A_apr00.pdf
    Last edited by NashuaTech; 07-17-2009 at 08:28 AM.

  3. #3
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    Jul 2009
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    Thumbs up Re: Venting a furnace

    I suppose I should have mentioned that this is not a chimney that goes through the house. It is attached to the side of the house, so that the furnace is vented from the side of the basement and then up.

    That's why we're looking at what other options are available to us, since it will be something easier to tear down and replace.

    I'm attaching a photo of this old thing. Not a great photo, but you can see where the location is.
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  4. #4
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    Default Re: Venting a furnace

    After speaking with Lennox, they told me we could use standard double-wall pipe as an alternative to the masonry chimney. After digging around, I found this:

    http://www.ventingpipe.com/mediabase...ions/Bvent.pdf

    Great diagrams, but it doesn't show anything about building this double-wall pipe on the exterior of the house. Can it be done?

  5. #5
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    Feb 2008
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    Default Re: Venting a furnace

    GF08:

    IMHO it would look unsightly if installed along the exterior of the house---it is often done in commercial applications, but it would detract from the home's appearance if done at a residence.

    A similar dilemma exists---if the masonry chimney is in half-decent structural shape, it can be left in place indefinitely & the metal double-wall installed somewhere thru the roof---otherwise, the masonry would have to be removed & that whole side of the house would probably have to be resided with vinyl, or whatever is on there now, so a good color match could be achieved.
    Last edited by NashuaTech; 07-19-2009 at 02:17 PM.

  6. #6
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    Jul 2009
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    Default Re: Venting a furnace

    At this point we're not concerned with how pretty something looks. We've bought an old house that hasn't been kept up for many years. A pipe on the outside is the least of our concerns. We're talking about safety and functionality at this point. If we can put the pipe on the outside, and then later on, when we reside the house, build a "covering" of sorts for it, great.

    We're looking at the best, safest and most inexpensive way to vent our furnace. Cosmetics be damned! That's a future expense.

  7. #7
    Join Date
    Nov 2008
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    Default Re: Venting a furnace

    Just curious...have you priced the new chimney. From the picture, I would guess it is about $2K to $3K to replace using the same material; and assuming you are not rebuilding anything inside; basic venting for furnace.

    Alternatively, the double-walled piping from your furnace through the roof will also work. I don't think you can vent an 80% efficiency furnace through the wall...but check with your local inspectional department on proper building codes in your area.

  8. #8
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    Jul 2009
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    Default Re: Venting a furnace

    While we have not had anyone come out and look, we've sent multiple pictures to some contractors. One said they estimate $850 to repair. Another said $2200 to replace (16').

    While $2200 isn't a huge amount of cash in the great scheme of home repair, we just don't have that right now as we just bought the house and have spent the money replacing the furnace, the electrical, and some of the plumbing. We are looking at something we could do ourselves to save on costs, or at the very least buy materials and pay someone the labor.

    It just is odd that there seems to be only one way to vent an 80% furnace. This crumbling chimney might have been fine for the furnace back in 1959, but something more efficient and compact has to have come along by now for modern furnaces.

  9. #9
    Join Date
    Nov 2008
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    55

    Default Re: Venting a furnace

    Another option: Run a double-walled pipe out the side of the house from the basement up to the roof line (above the chimney level). Run the pipe next to the chimney and box it in. You will have to check code, but it should basically do the same thing as running the pipe from the furnace straight up through the inside of the house (interior walls) through the roof. Except you do not have the cost associated with running a pipe through the middle of your house.

    From a cost perspective, pretty inexpensive solution. But you will need to check local code to make sure it is OK. Esthetically not ideal...but if you need something.

    Just a thought.

  10. #10
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    Jul 2009
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    Default Re: Venting a furnace

    This is exactly what we thought could be done, and I believe that's what the Lennox rep indicated. We already have the exterior chimney, thus the hole in the wall. It should just be a matter of replacing one thing with another.

    I'll have to stop into the township offices tomorrow to see what we can and cannot do. We don't live in a structured (pre-planned) neighborhood, so we may be able to get away with more.

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