Is my Heat Pump Too Smal
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  1. #1

    Is my Heat Pump Too Smal

    First the facts:
    location: Central Indiana
    Home size: 2800 sq ft about 2000 down and 800 up.
    Construction: Sip hybrid (downstairs and center core section all SIP panel with stick frame in the upper two wings)
    Heat Pump Size: 3 ton Trane XL16i with variable speed blower

    The Story:

    In February I had a new Heat pump installed at my new home. Initially we had to have several service calls because the heat pump and Aux heat were not able to keep up with the bitter cold (below 15 degrees). To fix they they ended up having to install an extra bank of heating elements to keep up.

    When summer came around, and cooling season hit, we found that the system could not maintain a temperature of 73 degrees when the temp hit 85 or more outside. To fix this, they came back and raised the fan speed on the variable speed blower to be at its highest setting. This has worked to make the house maintain temp even when it is 90 out, provided no one is home and not activity goes on in the house.

    However, This only works if we do not cook, have guests over, or turn on the can lights in the kitchen. If we do these things, the temp will go up 1 or 2 degrees (or more if we have a party of people), and the system cannot recover to its set point for several hours (usually around midnight after the sun has been down for a while, which tells me it is the drop in temp oustide that really is cooling)

    For example, On Saturday, when I got up the thermostat was set at 73 and it was showing 73 inside and 83 outside. I did some cooking in the kitchen and started the dishwasher which resulted in the temp going up to 74.

    I then turned the thermostat down to 71, to be sure that the blower would kick on high asap. However, the temp remained at 74 from 10 am to a bit after midnight on a day that was mostly 86 (although a bit humid) and cloudy.

    To me, this all speaks of a system that does not have the ability to cool the house in anything other than ideal conditions.

    Is my heat pump too small?

    Also, my HVAC people keep trying to tell me that i will only be able to cool 15 degrees below what the outside temp is. Which makes no sense to me. I've never been in a house that could not go below 75 if it were 90 or 80 when it is 95. Is this just BS?

  2. #2
    Join Date
    Aug 2003
    Location
    Lincoln, Nebraska
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    How did they size the unit. They should have or need to run a manual J to see just what the house load is. You should be able to get a copy of this from them. If they just did from square footage it is most likely not right.

    The 15 difference they are telling you about is not true either.

    Mabey they have somthing wired wrong also not letting the unit go to second stage for cooling. Have them back to make it right.
    Its a good Life!

  3. #3
    Quote Originally Posted by m kilgore View Post
    How did they size the unit. They should have or need to run a manual J to see just what the house load is. You should be able to get a copy of this from them. If they just did from square footage it is most likely not right.

    The 15° difference they are telling you about is not true either.

    Mabey they have something wired wrong also not letting the unit go to second stage for cooling. Have them back to make it right.
    He did it solely off square footage. I Think that the huge height/size of the great room is what it throwing his "rule of thumb" figures.

    They have been out and check the wiring, the temp drop (which is a good 19 degrees from input to output), and several other things. Last time they were out, they did adjust the airflow output to the max that the 3 ton can do.

    That gave us about 200 cfm more, and has helped, but no matter what the temp is, if i lower the temp on the thermostat, it takes forever to drop 1 degree. usually hours.

    I am too the point, i am ready to give them the ultimatum, either put a 4 ton condenser in, or you can take the whole damn thing out and refund my money. (which fortunately is guaranteed for the first year).

    I just want to be sure that i am being reasonable first.

  4. #4
    Join Date
    Jan 2004
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    Lancaster PA
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    An A/C can be sized to do about any temp difference between indoor and outdoor you want.
    The rule of thumb is what got you/him in trouble.

    Are all your can lights sealed.
    Has the duct work been checked for leakage.

    Before you just have them slap in a 4 ton, that you could end up having ven worse issues with.
    Get a load calc done!!!
    Oversized 2 stage units don't always dehumidify too good if they are over sized.
    Your duct work may also need to be changed to handle to the increased air flow of a 4 ton unit.

    I can maintain 72° in my house when its 98° outside.
    So the 15 degrees is BS.

    Taking a long time to drop 1° is not unusual for a 2 stage unit.
    You may be better off with a single stage 3.5 ton unit.
    Most combinations of the 15i will provide better heat then the 16i.
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  5. #5
    Quote Originally Posted by beenthere View Post
    An A/C can be sized to do about any temp difference between indoor and outdoor you want.
    The rule of thumb is what got you/him in trouble.

    Are all your can lights sealed.
    Has the duct work been checked for leakage.

    Before you just have them slap in a 4 ton, that you could end up having ven worse issues with.
    Get a load calc done!!!
    Oversized 2 stage units don't always dehumidify too good if they are over sized.
    Your duct work may also need to be changed to handle to the increased air flow of a 4 ton unit.

    I can maintain 72° in my house when its 98° outside.
    So the 15 degrees is BS.

    Taking a long time to drop 1° is not unusual for a 2 stage unit.
    You may be better off with a single stage 3.5 ton unit.
    Most combinations of the 15i will provide better heat then the 16i.
    They installed all the duct work when they put it in and have checked that too. One of the techs said that there was definitely enough duct work to handle a 4 ton unit. (he was the first service guy to come, and his opinion was that it was undersized)

    What would you consider to be a normal, reasonable time for a 2 stage to generate a 1 degree drop?
    I would think an hour would be reasonable, if not generous.

  6. #6
    Join Date
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    That depends on how the unit is sized.

    Im my own house. My unit is single staged. And if I try to drop 1 degree. It takes over an hour on average temp days, and can take 2 or more hours on hotter days.
    Mine is set up to remove a lot of moisture.

    Yours is 2 stage, and is trying to drop temp running in low stage. So it will take hours.

    I strongly doubt, that your contractor installed a duct system sized for 4 tons, when he was installing a 3 ton unit.
    That tech was probably using a rule of thumb. Which is what got you into this situation to begin with.

    There is also a good chance your stat isn't set up right.
    I would set it up to go to second stage quicker, and finnish the cooling cycle on second stage, when its hotter outside.
    Depending what stat they used, you may need another stat to do that.
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  7. #7
    Join Date
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    It would depend on how the 2 stage was set up. If on a 2 stage thermostat then it could take a long time or run for hours to maintain temperature on first stage. This would be for comfort and would remove humidity the whole run cycle. Most thermostats will not kick into second stage unless the temp is 1.5 to 2 below set point.

    Remember that a 2 stage unit is more for comfort than energy savings. As stated have a manual j run. Otherwise everyone is just guessing on the size.
    Its a good Life!

  8. #8
    Quote Originally Posted by m kilgore View Post
    It would depend on how the 2 stage was set up. If on a 2 stage thermostat then it could take a long time or run for hours to maintain temperature on first stage. This would be for comfort and would remove humidity the whole run cycle. Most thermostats will not kick into second stage unless the temp is 1.5 to 2° below set point.

    Remember that a 2 stage unit is more for comfort than energy savings. As stated have a manual j run. Otherwise everyone is just guessing on the size.

    That is why i turned the thermostat down to 71 degrees (- 3 degrees) to try to help it recover, which did kick the fan on high, and it ran run 14+ hours before it went down 1 degree. That seams wrong to me.
    Last edited by jackfalstaff; 07-21-2008 at 12:34 PM.

  9. #9
    Quote Originally Posted by beenthere View Post
    That depends on how the unit is sized.

    Im my own house. My unit is single staged. And if I try to drop 1 degree. It takes over an hour on average temp days, and can take 2 or more hours on hotter days.
    Mine is set up to remove a lot of moisture.

    Yours is 2 stage, and is trying to drop temp running in low stage. So it will take hours.

    I strongly doubt, that your contractor installed a duct system sized for 4 tons, when he was installing a 3 ton unit.
    That tech was probably using a rule of thumb. Which is what got you into this situation to begin with.

    There is also a good chance your stat isn't set up right.
    I would set it up to go to second stage quicker, and finnish the cooling cycle on second stage, when its hotter outside.
    Depending what stat they used, you may need another stat to do that.
    They did set the thermostat up to go to 2nd stage quicker (infact it runs most of the time on second stage) when it is hotter outside.

    The thermostate is a Honeywell vision pro IAQ...

    I wouldn't be surprised if the duct wasn't sized too large to start with.. the velocity of air coming out of the registers, even on high, seem very low to more, compared to other systems i have known... And we definitely need higher velocity upstairs than we have now..
    Last edited by jackfalstaff; 07-21-2008 at 12:34 PM.

  10. #10
    Join Date
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    Then missed his size by ½ a ton, or so.

    You said you hear it go to second stage.
    Does that mean you hear more air noise when it goes to second stage?


    If your current duct system is at .7" TESP at 1200 CFM. And you have a 4 ton installed on the same duct work, and move 1600 CFM through it. Your static will increase to over 1.2".

    That is too high, and will give you noise from your ducts and registers.

    If they set it to 350 CFM per ton, for a 4 ton, your static will still be around .95"
    Better then at 1600, but still a bit on the high side.
    But easier to make duct modifications and return and or supply additions.
    And shorten the life of your VS blower motor.
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  11. #11
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    Atleast they used a good stat.
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  12. #12
    Quote Originally Posted by beenthere View Post
    Then missed his size by a ton, or so.

    You said you hear it go to second stage.
    Does that mean you hear more air noise when it goes to second stage?


    If your current duct system is at .7" TESP at 1200 CFM. And you have a 4 ton installed on the same duct work, and move 1600 CFM through it. Your static will increase to over 1.2".

    That is too high, and will give you noise from your ducts and registers.

    If they set it to 350 CFM per ton, for a 4 ton, your static will still be around .95"
    Better then at 1600, but still a bit on the high side.
    But easier to make duct modifications and return and or supply additions.
    And shorten the life of your VS blower motor.
    I can hear it when i am next to the closet with the air handler, yes. Not really from the ducts. In fact, when you put you hand over the ducts, when it is in stage 2 it is hard believe that it is on high.

    Frankly, I wouldn't mind some noise if it would work better, to where i had confidence in it.

    It may be that my expectations are wrong from this system. I expect it to heat to the temp that i set it at, and cool to the temp i set it at, regardless of interior or exterior conditions (within reason)

    I just don't ever remember, growing up, that it took forever to cool and wouldn't keep up on hot days or when you have some people over or cook.

    To me, that defeats some of the purpose of the cooling system. I'm not saying i am not comfortable most of the time. I just want to be sure that I am not settling for a system that is not working well enough, considering the considerable investment.

    If this is how it is supposed to work, i can accept that, but neither my wife or I feel that it is working as well as we thing it should.

    which is why we are asking you fine people, if our expectations are correct. :-)

  13. #13
    Quote Originally Posted by beenthere View Post
    At least they used a good stat.
    That's the thing, i feel like they know what they are doing, with the exception of assuming that the unit is adequate, without question.

    But at this point they have checked everything to make sure its working, tweaked the settings on the units and thermostat, and we are closer, but the changes are maxed out now. And i still feel like it barely does its job.

    Is that normal?

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