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  1. #1
    Join Date
    Oct 2003
    Posts
    48

    High Seer added to existing furnace

    I have a customer that was quoted a 15 seer Carrier A/C and HP system added to his existing gas furnace. His home is new and he would like to keep his old furnace. I told him I did not think one could achieve More than 14 seer without replacing his furnace with a variable speed option. I know that ARI is the authority on this but I don't know the model of the unit he is quoting. We have also seen head pressure problems on high seer heat pump add ons to existing builder type gas furnaces with standard blowers. Any input would be appreciated.

  2. #2
    Join Date
    Jul 2004
    Location
    Massachusetts
    Posts
    6,841
    First off, you have to recognize the fact that a Carrier, Trane, Rheem, York or whoevers unit rated 14, 15, 16, whatever SEER, it's just a label. I've seen Goodman units rated 13-SEER and if you couple them with the right coil, get 14 or 15-SEER!! So the SEER LABEL is different than the actual performance number. I was amazed to see a higher effeciency rating on a Bryant Evolution HP with an 80% paired furnace than the same HP on a 95% paire furnace! Don't know why but suspect there's a lower airflow from the recuperative coil in the 95% that changes things. Heat pumps perform properly when they have a proper charge, a properly sized indoor coil and proper airflow. Upset the applecart with some deviation and you easily be headed for trouble, regardless of the efficiency rating. What I would definitely recommend against would be installing a 2-stage HP on a furnace with a multi-speed motor. If you can't control the blower speed with a 2-stage HP, I'd move on down the efficiency scale to a 1-stage HP or replace the furnace with one having a variable speed blower.
    If YOU want change, YOU have to first change.

    If you are waiting for the 'other guy' to change first, just remember, you're the 'other guy's' other guy. To continue to expect real change when you keep acting the same way as always, is folly. Won't happen. Real change will only happen when a majority of the people change the way they vote!

  3. #3
    Join Date
    Jan 2004
    Location
    PA
    Posts
    68,777
    He will not get the humidity control from a standard blower thet he would with a VS blower.
    Also, he will have a lot cooler air blowing out the registers in first stage heating from the heat pump.
    Basically, he won't be getting the comfort he payin for from the 2 stage heat pump.
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  4. #4
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,600
    With single stage, you just lose efficiency. The "Performance 15" A/C unit with standard blower runs 13.50 to 14.00 SEER for example. It's a waste of money unless you just want a particular outdoor unit but won't hurt anything.

    With 2 stage on a standard blower you really get into the problems with the blower not doing exactly what the mfr designed the system for. I'd never suggest doing that.

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