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  1. #1
    Join Date
    Dec 2010
    Location
    South Florida
    Posts
    4

    Max temp at ducts

    I live in south Florida. I recently had a Rheem 5 ton a/c system installed in my home (models 14AJM56A01 and RHLLHM60xx). I was told that they system also includes a 10KW heat strip.

    During the heat cycle, the temperature coming out of the closest duct never goes above 88 degrees. This does not vary based on internal temperature (i.e. 68 or 78 degrees) or external temperature (i.e. 40 or 70 degrees). I was told that this is because the system includes a heat pump, however, I would think that since the system includes a heat pump that the interior heat gain would decrease as the outside temperature drops. All my tests show that nothing affects the temperature coming out of the ducts (consistently 88 degrees).

    Can someone tell me if this is normal? Shouldn't the temp of the air coming out of the ducts be hotter when it is hotter in the house or when it is hotter outside?

    Also, I can't find the technical specs for this unit, can someone tell me what the delta t is for my unit?

    thanks.

  2. #2
    Join Date
    Mar 2007
    Location
    Myrtle Beach, SC
    Posts
    2,919
    You should get a certain temperature rise based on the outdoor temperature.

    If it is 15 degrees outside, the indoor unit should raise the temperature about 13 degrees.

    If it is 65 degrees outside the indoor unit temperature rise should be about 33 degrees.

    That assumes proper air flow and proper refrigerant charge.

    That is without any heat strips being on.

    Temperatures at the registers will be less depending on duct location and duct insulation.
    Remember, Air Conditioning begins with AIR.

  3. #3
    Join Date
    Dec 2010
    Location
    South Florida
    Posts
    4
    I recognize temperatures will vary depending on location, therefore I am testing at the closest duct. Since the install was only a couple of weeks ago I am assuming that pressures are correct. Everything is new, including the copper between the air handler and the compressor. There has been no decrease in heating capacity since the install. Same for cooling.

    Based on my tests, it doesn't matter what the temperature is outside. The air coming out of the closest duct is always 88 degrees. This is true if the outside temp is 40 degrees or if it is 70 degrees. The same is true for indoor temperature, I have tested starting indoor temperatures from 67 degrees to 80 degrees. Additionally, this is also true if the emergency heat is turned on or off. All of these statements have been verified using a recently purchased thermometer.

    It just doesn't seem right (to me) that the air is always 88 degrees.

    The thing that I am concerned about is whether 1) both the heat pump and the heat strips are working, 2) if only one of them are working, or 3) neither are working properly. Right now, all I can say to the installer is that I don't think it is working correctly, but I have no basis for my conclusion. My previous (20 year old unit) had much hotter air coming out of the ducts. If I'm wrong I'd like to know that too, I'd be happy to know that everything is working correctly.

  4. #4
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,778
    Then I'd put the new thermometer in the oven of some place where I know the temp is 100 degrees. And see if the thermometer has a problem.

    Could be that the supply your checking has a problem.
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  5. #5
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    33,934
    You ain't gots a heat pump

    Anyway 10kw on a 5 ton air handler won't have much of a temp rise. I'm too lazy to calculate it but 88 out the vents may not be wrong. It should vary with return air temp though.

  6. #6
    Join Date
    Mar 2007
    Location
    Myrtle Beach, SC
    Posts
    2,919
    BaldLoonie is right. That is a straight AC condensor, not a heat pump. All you have is strip heat for heat. Not very efficient for heat.

    Of course in Florida, you may not need heat very often.

    Was your old unit a heat pump?

    Your new one is not.
    Remember, Air Conditioning begins with AIR.

  7. #7
    Join Date
    Dec 2010
    Location
    South Florida
    Posts
    4
    Based on what I know of the previous owners I doubt they spent the money for a heat pump.

    I have verified the accuracy of the thermometer against othe thermometers that I have on hand.

    The temp down here rarely goes below 35 degrees and we only use the heat for 15--20 days a year.

  8. #8
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,778
    Quote Originally Posted by BaldLoonie View Post
    You ain't gots a heat pump

    Anyway 10kw on a 5 ton air handler won't have much of a temp rise. I'm too lazy to calculate it but 88 out the vents may not be wrong. It should vary with return air temp though.

    Temp rise, as low as 16°F at 2000CFM, and as high as 20 at 1600 CFM.
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  9. #9
    Join Date
    Dec 2010
    Location
    South Florida
    Posts
    4
    I'd like to thank everyone for their help.

    I have determined that I was misinformed regarding the heat pump issue. I'm not sure how I feel about that at this point.

    Additionally, I have decided to assume (at this time) that everything is ok regarding my heat due to the increased CFM of my unit versus my old unit. Although, I still have not found a reasonable explanation to explain why the temp coming out of the closest vent is always 88 degrees. My understanding of HVAC says that the temp should vary with the intake temp (i.e. delta T).

  10. #10
    Join Date
    Jan 2011
    Location
    greenville , sc
    Posts
    718
    Quote Originally Posted by BaldLoonie View Post
    You ain't gots a heat pump

    Anyway 10kw on a 5 ton air handler won't have much of a temp rise. I'm too lazy to calculate it but 88 out the vents may not be wrong. It should vary with return air temp though.
    im pretty lazy too ,but it somewhere around 3.5 to 3.8 hair dryers

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