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Thread: Size Hvac unit

  1. #1
    Join Date
    Jan 2007
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    54

    Size Hvac unit

    Have a new 2044 sq ft heated brick home w/ tyvek wrap house that has 207 sq ft double pane low e windowws, 84 sq ft outside door space, 14' vaulted ceiling in 21' x 18 ft rm, 12 ' vaulted ceiling in 10' x 11' rm rest of ceiling 8' h . A 3 1/2 Rheemn RRNA-B042JK10E ton gas pack was installed heat 100,000 BTU and Cooling 42,000 btu. My problem is that the heat runs for about 5 min then off about 17 min. seems its always cold in the living room where the vaulted ceiling is.
    Themostat was placed in the hall over the return duct where all the bedrooms are located. Should this be moved to the living room. I was told by the HVAC installer he could cap off something on the heat exchanger for less btu,s so it would run longer does this seem logical, or is unit just to big for house?

  2. #2
    Join Date
    Nov 2007
    Location
    Tucson AZ
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    166

    Fans

    You need to mix the air in the living room - all your warm air is in a bubble at ceiling level.

    A pair of ceiling fans blowing down should make a big difference. Moving the thermostat will just make other areas too hot, and while derating the furnace will make it run for longer periods. The only benefit from that will be better mixing of the air generally (which might help a little).

    Focus on the living room where your problem is, and get the air there moving.

  3. #3
    Join Date
    Aug 2005
    Posts
    215
    Do you have just 1 return air in the hall for the whole house?

    The fans will help some, but how are the other rooms heating and cooling? are they to hot or cold?

  4. #4
    Join Date
    Jan 2007
    Posts
    54
    Have one return in hall and one in master bedroom other rooms seem fine because only 8' ceiling w/exception of one bedroom with 12' Vaulted ceiling. Seems 3 1/2 unit to big had another house this size only 3 ton?




    Quote Originally Posted by marlboroman View Post
    Do you have just 1 return air in the hall for the whole house?

    The fans will help some, but how are the other rooms heating and cooling? are they to hot or cold?

  5. #5
    Join Date
    Jan 2007
    Posts
    54
    Have one return in hall and one in master bedroom other rooms seem fine because only 8' ceiling w/exception of one bedroom with 12' Vaulted ceiling. Seems 3 1/2 unit to big had another house this size only 3 ton?

  6. #6
    Join Date
    Jan 2007
    Posts
    54
    Have one return in hall and one in master bedroom other rooms seem fine because only 8' ceiling w/exception of one bedroom with 12' Vaulted ceiling. Seems 3 1/2 unit to big had another house this size on

  7. #7
    Join Date
    Mar 2008
    Location
    Baltimore MD and Ridgebury PA
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    542
    Did the contractor perform a load calc (Manual J) when they sized and installed the system? On a related note, central returns are never as effective as individual returns for each room. That may not play a part in your problem but its not a good way to perform an install in a new home. Anyway, if they performed a proper load calc then either the supply to the living room is undersized or, as jeff520 stated, you need ceiling fans or some other method to push the warm air down from the ceiling.

  8. #8
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,286

    Increase the run time

    Quote Originally Posted by Bigdog8 View Post
    Have a new 2044 sq ft heated brick home w/ tyvek wrap house that has 207 sq ft double pane low e windowws,

    ... was installed heat 100,000 BTU and Cooling 42,000 btu.

    My problem is that the heat runs for about 5 min then off about 17 min. seems its always cold in the living room where the vaulted ceiling is.

    so it would run longer does this seem logical, or is unit just to big for house?
    Too Big

    Run time is 22.7%


    Run time should be > 70% when the Outside temperature is close to the Design temperature.
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  9. #9
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    68,064
    Did you have uneven room temps with the old unit.
    Contractor locator map

    How-to-apply-for-Professional

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

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