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Thread: New Furnace Advice Sought

  1. #1

    Default New Furnace Advice Sought

    A remodel (in the Pacific NW) we are considering would entail:

    - Removal of a chimney that wastes precious space in our tiny kitchen.

    - Replacing our _horribly loud_ and _stupidly placed_ gas forced-air furnace (combustion air supply PVC pipe actually blocks part of a doorway!) with a high-efficiency one that would be upstairs and hidden behind the living space's knee-wall pretty decent height there -- an old electric water heater used to be there till I removed it.

    If moved there, the furnace would still be directly adjacent to the chimney's location, just a floor up. Therefore ducting should be fairly easy:

    - hot air supply & return could go through a coat closet we'd gain in moving the furnace upstairs.

    - exhaust venting could still go through the chimney's roof penetration.

    I don't know if this is a "downside" of that location, but I'll mention that we had the house insulated last year, so there is a lot of blown-in insulation in the potential furnace location. I'd guess it's not a problem per se, but just an inconvenience during installation and we'd better just make sure that the insulation gets replaced/redistributed as well as possible after furnace install.

    Alternately, the furnace could be moved out to the utility room, as we are considering replacing the (possibly dying) gas water heater with a tankless one which would free up space. The utility room is a walled-in breezeway between the house and the formerly unattached garage, thus it is outside of the foundation and I am wondering about the difficulty of furnace ducting through it.

    I know my description lack a lot of context for y'all, but any advice (location & type of furnace, anything) is appreciated. Thanks.

  2. #2
    Engineer Furd's Avatar
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    Depending on just where in the Pacific Northwest your home is located a 90+% furnace may not save enough fuel to cover the additional cost over its lifetime.

    I don't know what you might consider as being "pretty decent height" but installing a furnace where it cannot be easily serviced is a big mistake. You need to be sure to adhere to all of the manufacturer's minimum clearances and for ease of service probably exceed the "recommended" clearances for service.

    I can't determine just what your plan was concerning the existing chimney but you cannot remove a masonry chimney from the bottom up as the lower part holds the upper part. You would likely need to remove the chimney from the roof down and if you desired to use the roof penetration for the new furnace then you would build a "chimney chase" around the existing penetration to enclose a type B vent, assuming you are using a gas-fired furnace.

    The supply and return duct work to your existing duct system would be no small job. Remember that most return ducts are woefully inadequate and that your extensions of both supply and return would likely be larger than the existing ducts.

    The blown in insulation would be far more than just an inconvenience, it would have to be contained, likely by building a furnace room enclosure and that too would be a restriction for installation and servicing of the furnace. You also need to make provisions for the entrance of combustion air to this furnace enclosure.

    In all of this planning you MUST take into consideration your local mechanical and energy codes. Moving a furnace absolutely requires a permit and inspection by the local Authority Having Jurisdiction.

  3. #3
    Master Plumber nhmaster's Avatar
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    I really like the Ruud or Rheem (same company) 90++ condensing furnace. Really nice, well made piece of equipment.

  4. #4
    DIY Junior Member tedfrk's Avatar
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    Quote Originally Posted by nhmaster View Post
    I really like the Ruud or Rheem (same company) 90++ condensing furnace. Really nice, well made piece of equipment.
    i second that real nice equipment,it is also nice to work on.most if not all the 90% furnaces i have installed suggest you have the furnace in a conditoned space.meaning somewhere the pipes wont freeze because they do produce condensation and alot of it.I dont understand why your existing pvc exhaust goes out through your masonry chimney,but if you move it up stairs you can get 2 plumbers roof jacks for the 2" pvc pipe,one exhaust and one intake.the furnace book tells you how far to keep them apart,and how far to keep things away from the furnace.you will want the pvc at least a foot higher then the highest snowfall you get,because if snow blocks the pipes your furnace will shut off.you will need to make sure you can have your pvc drain for the condensation drain somewhere inside depending on your codes there because that can freeze also if you run it outside.i would have a couple of estimates from local hvac companies and see how they would run the equipment.
    Last edited by tedfrk; 10-23-2008 at 07:42 PM.

  5. #5

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    The existing furnace uses galvanized exhaust (~85% efficient when new, but a service tech expected that it was less than 80% at this stage, more like 75%), not PVC, which is why it runs through the chimney. I just figured we'd go with a high efficiency furnace but hadn't done any number crunching on payback really. I figure energy costs will only go up, and furnace efficiency only goes down, so at some point I figure it'll pay off. Maybe not in our mild climate.

    Point taken about adequate installation requirements. I'd never consider doing something inadequate with such a pricey item. I'd definitely utilize a pro for that, though I'd be sure to let them know my goals to recover usable floor space in our house. The furnace would really be very close to it's current location, just one floor up, and on the opposite side of the chimney, so I really think that the ducting is doable.

    BTW, Currently there are only returns on the first floor. Is that the way it is usually done, or might there be a reason to have returns on each floor?

  6. #6
    Master Plumber nhmaster's Avatar
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    Better yet you can use a concentric vent that combines both exhaust and intake in one pipe.

  7. #7
    Retired Defense Industry Engineer jadnashua's Avatar
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    Ideally, each room that might have the doors closed would have a return. The air goes where it has the least resistance, and when you close the door, it's like trying to blow up a balloon...this means that balancing the system so you have even temps will change when any door is closed or opened.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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