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  1. #1
    Rashid Karimov's Avatar
    Rashid Karimov Guest

    Question A 95%+ furnace - new flue in a townhouse.


    I hope you don't mind a property owner posting a question.

    I own a townhouse in NE USA. The original gas furnace was nearing 20Y of age, so I started looking for replacement - concerned about fumes leaking through rotten core into the air supply and not waking up one day. Read a lot, found out that we have much more efficient furnaces available these days, found one I liked - a 95% efficient 95KBTU unit from Goodman.

    Before ordering it, found a list of installers (off Goodman's website) in my area, got in touch with one, discussed the tonnage, had an install quote and ordered the unit.

    The installation was pretty quick - it fit just fine into the space where the older unit was. The installer was very professional and very meticulous.

    But, when it came down to wiring up the exhaust flue, the gent told me he could not exhaust into the shared chimney (shared with the gas water heater), as it is against the code. So he ran a horizontal 4" exhaust PVC pipe, at slight angle and exhausted through the side. All very nice and neat - capped it with a 45 degree elbow, facing downward so that rain or snow could not enter and put a mesh cap on it, I guess so that a bird would not try to build a nest there. He tested everything and left.

    Few days after he left, I had neighbors question why is it I have this exhaust outlet sticking through the wall. I explained that the high efficiency furnaces require separate flues. Did some reading and discovered the only other alternative is to exhaust vertically - but that would have to be pretty high pipe (we can get a lot of snow), it has to be far from any verticals - so that the snow drifts dont build up etc.

    I was wondering if you know of a law that states that install code supersedes all the wonderful association bylaws - stating that if a flue requires a hole in common area, then a hole goes into the common area ?

    All of the owners will inevitably have to replace their furnaces too, pretty soon - as the heater cores are so worn out, I guess everyone would have to exhaust the same way mine is (all units are the same), but I could use some advice from experts here to try to pacify them in the interim. I am sure most of you are no strangers to how crazy it can get in some of the home owner associations

    The flue is high up and far from any walkways or areas where ppl might be. There're no windows or doors in the vicinity of the exhaust - they guy did do a very nice job.

    Thank you very much.


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    Last edited by Rashid Karimov; 07-29-2009 at 05:30 PM.
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  2. #2

    Default Re: A 95%+ furnace - flue in a tonwhouse.

    I'm sure Bob, or someone much smarter than me will be on here pretty soon, but 'til then.........

    Does the water heater vent directly into the chimney, or is the chimney acting as a chase?
    Is the chimney a masonry chimney?
    If the water heater vents directly into the chimney, then I recommend adding a flue liner (B vent) for the water heater that runs all the way to the top of the chimney. It is likely that the original masonry (I am making assumptions here) is over sized for just the water heater.
    If that chimney is just acting as a chase, then I am pretty positive that the furnace can share this chase (original masonry chimney) with the water heater flue pipe, as long as the PVC furnace exhaust vent is at least 1" away from the B vent.

    There are a lot of unknown variables here.

    It may help if you posted pictures.........

  3. #3
    Rashid Karimov's Avatar
    Rashid Karimov Guest

    Default Re: A 95%+ furnace - flue in a tonwhouse.


    appreciate your reply. I will post a pic tomorrow as it is too dark outside at the moment.
    The old gas furnace was sharing the chimney with the gas water heater. The chimney is tin all the way to the roof - there's no fireplace or anything like that that uses the chimney, now that the new furnace has a dedicated exhaust PVC pipe, outside of the water heater (80% 40Gal unit).


  4. #4
    Ron Bibler's Avatar
    Ron Bibler Guest

    Default Re: A 95%+ furnace - flue in a tonwhouse.

    Its not required to vent out the side wall. You can have a new vent system installed next to the old vent and up to the attic and then install a new roof jack and then repair the roofing materials.

    Other condition may be required. Further inspection of the walls. You may need to cut a unknown section of wall or attic/roof supports/framing.
    This would require building permits, plans and engineering

    If your HOAhome owner associations requires it in another place well you known what you will need to do

    I think what the young man did for you was save you a bunch
    of $ $ $ nice guy.



  5. #5
    Join Date
    Mar 2007
    Near Philly, Pa.

    Cool Re: A 95%+ furnace - flue in a tonwhouse.

    Sounds like you have a new Category IV furnace mechanically vented out the side of the house with no provision for makeup air. This may be allowed by the furnace mfr. but can depressurize the Combustion Appliance Zone (CAZ) and pull carbon monoxide back down the WH vent, which sounds like B-vent. Since the WH is being orphanned into a 20 y/o vent, you should get a Level II inspection to determine if the existing B-vent is adequate for just the WH, the location of the furnace vent termination according to the listed installation instructions and applicable codes, and makeup air requirements.

    Yes, you cannot vent a CAT IV into a B-vent or chimney---it would simply vent out the seams of the vent connector and draft hood back into the house and kill you, that's all.

    You must consider the codes, listing, AND the Homeowners Assn. rules. If they don't allow the sidewall vent termination then you must vent vertically. To do that, you must find enough space to vent up alongside the B-vent while maintaining your 1" clearance to combustibles and firestopping w/ fireblocking at the ceilings & attic. The appliance installation instructions will address vertical venting requirements and limitations. However, you must get a second pipe in there for combustion air into that furnace. If it turns out you don't have the room for all three pipes, you could run both PVC pipes up the chase cavity after removing the B-vent then switch to an electric WH.

    Townhomes can be tricky because of the condo rules and setbacks. Since you're in the northeast, you have to worry about snow drifts, esp. in Mass.

    Get a low level CO monitor for your home: NSI 3000 or CO Experts.


    Keep the fire in the fireplace.

  6. #6

    Default Re: A 95%+ furnace - flue in a tonwhouse.

    Yeah, that's what I meant. What Bob said......


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