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  1. #1

    Duel Fuel Question

    Hey guys and gals I have a question about duel fuel....

    Lets say I have a heat pump with a gas furnace as my aux heat .... Here is my question .... I have heard in the past that these systems do not use defrost because the hot air (from furnace as aux in defrost) will be too hot for the indoorcoil as it is in defrost and will cause the coil to split .... Now I know about balance point but even at 40 degrees OD temp the outdoorcoil will be much colder then that and will be possible for ice to form so defrost will be needed correct? .... you can correct me if im off base here but I was just wanting to know that truth ... thanks all

    Ziggy

  2. #2
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,584
    I have gas heat come on during defrost. Never had the high pressure switch trip from it. The dealer can wire a sensor in the plenum to shut off the gas if the air gets too hot. We did it that way in our old office when the back up was oil.

  3. #3
    Join Date
    Aug 2007
    Location
    Northern VA 38 degrees N by 76 degrees W
    Posts
    5,062
    The gas furnace does come on for defrost and does not burst coil.

  4. #4
    Ok Thanks guys !! .... I was just wondering ... I forget where I heard that once but someone told me that it would run the suction pressure thru the roof lol ... being that its running in a/c mode to melt the ice off the OD unit and the ID coil would be absorbing all that heat & burst the coil... Thanks again all for setting me right on that one =)

    Ziggy

  5. #5
    Join Date
    Jan 2004
    Location
    PA
    Posts
    68,748
    Next time someone tells you that.

    Remind them that.
    If the heat pump shuts down. The refrigerant sitting in the coil still absorbs all that heat.
    And the pressure will be higher then if it was running.
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    How many times must one fix something before it is fixed?

  6. #6
    Thanks Beenthere,

    One more question ... on duel fuel does the furnace get cycled on and off to help supplement the heating of the house like the aux (strip heat) heat does? ... Or does the heatpump have to cycle off or enter defrost before the furnace can run? ... I guess what im asking is if the furnace runs while the heatpump is in heat mode will this cause head pressure problems? .... All I have is a normal heatpump but have been looking at some duel fuel setups ..... I'm guessing you have to have a special thermostat and that does a lot for a duel fuel system

    Ziggy

  7. #7
    Join Date
    Jan 2004
    Location
    PA
    Posts
    68,748
    Once the furnace comes on because of a heat call, the HP shuts off.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

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