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Thread: New Furnace Advice

  1. #1
    DIY Member sctclimbs's Avatar
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    Default New Furnace Advice

    We are looking to replace our furnace. It is a Goodman 100,000 BTU, 80% efficient model. It is actually working fine but is 15 yr. old. We are doing a remodel and thought we'd just go ahead and do the furnace, plus a friend of mine would love to replace the behemoth he has in his basement with ours in a fix and flip he is redoing.

    In searching this awesome forum I have gained a lot of great information and wanted to see if there is anything else I'm missing. So please correct me if I'm wrong.

    1. The best furnaces are 90%+ efficient, have variable speed blowers and closed combustion chambers.

    2. We will want to get as small a furnace as necessary b/c a bigger furnace will have shorter run times and be less efficient and create bigger temp. swings in the home, making it less comfortable.

    3. We should have a Heat Loss Analysis done to figure out the ideal size of furnace to use.

    4. Recommended models: Trane, Rheem (ANy others???)

    Any other advice???
    How much of this can I do myself as far as removing the old and installing the new one and how much should I leave to the pros?
    Our house is a ranch with a finished basement. The thermostat is on the main floor. When is cold out the basement tends to be probably 10 deg. cooler than upstairs, anyway to remedy this?

    Thanks

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    Forced air systems can be zoned, but that can add significantly to the costs. If the ducts don't have and dampers in them, they can be added. balancing the airflow can help, but without zoning, may not solve the problem. If there isn't a good air return duct in the basement, add one. Trying to blow air into what amounts to a semi-sealed room is very inefficient - that's what happens if there is no return. If you run the fan continuously (not a bid deal with a variable speed fan since the default speed is quite slow), it helps. Also, if you run more heat into the basement and let the natural convection take it upstairs, it sometimes works well. If the house is tight, this won't work. I rarely close doors, so it works for me.

    I also found that a high return works really well in the summer when running the a/c...it takes the hot air out from the ceiling area and recircuilates it making the whole thing more comfortable. in some houses I've been at, they extend the ductwork up the wall and have two registers; one at the top and one at the bottom. Use the lower one in the winter and the upper one in the summer.

    I don't have enough experience with the various brands to recommend one over another. Some of that will depend on what is available locally, and finding an installer/maintainer you can trust.

    If you aren't making much of a change, then a R&R of the old one may not save you much. Check with the installer.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3
    DIY scratch-pad engineer leejosepho's Avatar
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    Quote Originally Posted by sctclimbs
    The best furnaces are 90%+ efficient, have variable speed blowers and closed combustion chambers.
    Yes, I believe so, and they are also the least-likely to be repaired by a typical homeowner.

    Quote Originally Posted by sctclimbs
    How much of this can I do myself as far as removing the old and installing the new one and how much should I leave to the pros?
    To be sure nothing gets damaged or removed unnecessarily, I would have the installer take an overall look before you might do the removal of the old furnace, but keep in mind there are gas and power lines involved. Personally, I would leave the entire job to a communicative pro.

  4. #4
    DIY Senior Member Nate R's Avatar
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    I love that my Goodman is simple enough for me to be able to work on it. Had 2 problems with, 1 install related, and one due to a loose fuse. Was nice to be able to diagnose them myself. If what's said above about the most efficient furnaces is true, Dunno if the lower heating costs would be worth the higher repair bills.

    But then again, it was an upgrade for us to get an 80% efficient Goodman. Better than the 30+ yr old Sears that would've killed us within minutes if the flue got at all obstructed. (Pegged the inspectors meter at over 1000 PPM CO!)

  5. #5
    Retired Defense Industry Engineer jadnashua's Avatar
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    A 94% efficient furnace is 17.5% more efficient than an 80% one...take your heating costs and take off 17.5% and see how long it will take to regain the difference in costs. With a variable speed fan, you'll be more comfortable (hard to put a price on). There are a few more safety devices and a fan for the forced exhaust on this type of furnace, but if you can read a schematic, not much harder to troubleshoot. Maintenance is about the same. You may also be eligable for both federal tax credits and utility company rebates, which will reduce the difference in costs. My gas utility gave me $800 rebate for putting in a high-efficiency boiler and another $300 for an indirect WH. Some give good rebates for HE furnaces as well. You'll get nothing back from them on an 80% job.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  6. #6
    DIY Member sctclimbs's Avatar
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    Thanks for the info.!

    I've started to get some quotes on furnaces. One was for $3600 installed on a 70K 90+efficient furnace but was only single stage and single speed. Guessing $4000 or more for a two stage, dual speed. Of course the cheap skate in me has been looking on online and there are Goodman 2stage, dual speed, 90-95% efficent units for $800-1400.
    I've had a hard time finding what you would pay just for a furnace, retail. Is that price typical or too good to be true?

    Would I really expect to pay $2000+ for installation?
    Last edited by sctclimbs; 10-21-2007 at 03:12 PM.

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