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Thread: Hot plenum

  1. #1
    Join Date
    Feb 2013
    Posts
    1

    Hot plenum

    My father recently had a new American Standard furnace installed at his log house and the plenum is hot to the touch. There are two furnaces heating the place and the other is a Goodman and doesn't get hot. The furnace that the AS replaced was also a goodman and the HX cracked after only 7 years. Could there be an issue with the ducting on that side of the house?

  2. #2
    Join Date
    May 2006
    Location
    Philadelphia, PA
    Posts
    1,374
    Yes.

    Are the units sized properly?
    Climate Control Solutions for your Home or Office

    Serving Northeast Philadelphia and Surrounding Areas

  3. #3
    Join Date
    Nov 2009
    Location
    Central Virginia
    Posts
    146
    Doesnt sound like the plenum is insulated. Or lined.

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  4. #4
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    The ductwork coudl be undersized for that size furnace.... or the furnace is oversized. Very common for contractors to not do a laod calculation and replace a 80k 70% furnace with a modern 80k BTU 93% furnace. The old unit only put out 56k BTU't, the new one 74k BTU's. The old one may have also had a 70F max temp rise, and therefore only needed 750CFM. The new unit is struggling to get even 900CFM, but needs 1100 and so it's running too hot, possibly cycling off the high limit.

    Whevenever you hear about a early HX failure, the first thought it that it overheated due to lack of airflow. The second is improper combustion, and a third is operating hte unit at low temperatures. You shouldn't operate a furnace with return air temps under 55-60F... especailly if its' oversized and short cycles.

  5. #5
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
    Posts
    2,596
    Quote Originally Posted by Leafs13 View Post
    My father recently had a new American Standard furnace installed at his log house and the plenum is hot to the touch. There are two furnaces heating the place and the other is a Goodman and doesn't get hot. The furnace that the AS replaced was also a goodman and the HX cracked after only 7 years. Could there be an issue with the ducting on that side of the house?
    Hot plenum and cracked HX.....I bet it's short on return (most likely) and possibility the supply as well.

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