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  1. #1

    Old 110,000 BTU Luxaire to 45,000 BTU Rheem?

    Hi everybody; I'm looking to upgrade an older furnace in my house to take advantage of the 30% tax credit. The house is a 2-story ranch built in the 1950's. The 2nd story of the ranch was added on later with completely seperate duct work so I have a furnance upstairs (now a Rheem 90). The house in total is 1800sq feet, though you could say 900sq feet is being handled by the upstairs furnance. The house is located in southern Michigan. The basement is partially finished and runs the total sq. feet of the house.

    The furnance appears to have been installed in 1979 and is a Luxaire. The panel says it is 110,000 BTU in and 88,000 BTU out (80% efficient).

    The house has newer Andersen windows, but no insulation in the walls. I've recently upgraded the insulation in the attic to R-49 with blown in cellulose.

    The contractor has quoted me a 45,000 BTU 2-stage 95% efficient Rheem unit (RGRL). This is obviously half the BTUs of my previous furnance (even more when running in its low mode), but perhaps that one was oversized from the get-go. The heat has been fine in the main-level, but I wouldn't say it's been especially overpowering.

    Does 45,000 BTU sound like enough in this situation?
    Last edited by dj1s; 07-18-2009 at 03:13 PM.

  2. #2
    Join Date
    Mar 2005
    Location
    Houston, Texas
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    Don't guess, know what it takes:

    http://hvaccomputer.com/talkref.asp

  3. #3
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,455
    I wouldn't think a smart contractor would undersize. You'd be pissed at him!

    And yes, isn't usual to downsize quite a bit. In the old days, bigger was better. Plus you have new windows & ceiling insulation.

    The RGRL is a nice furnace.

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