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Thread: A/C sizing

  1. #1
    Join Date
    Mar 2005
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    7

    Confused

    From all I've been told, any house with less than 1600sq ft. would be unwise to use 2ton A/C as it will not properly remove humidity and result in a loss of the SEER value, due to constantly going on and off....any thoughts on this??

    Also, rough rule of thumb is given as 1Ton per 1000sq ft??

  2. #2
    Join Date
    Jul 2004
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    midwest
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    Somebody is telling you wrong.

  3. #3
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    Sep 2002
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    South Dakota
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    Guessing and/or using so called rules of thumb do not produce good results. Your need to read this.

    http://www.hvac-talk.com/vbb/showthr...threadid=33866


    A proper load calculation is the ONLY way to properly size a system!

  4. #4
    Join Date
    Dec 2002
    Location
    Houston,Tx.
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    16,122
    Originally posted by sd47
    Also, rough rule of thumb is given as 1Ton per 1000sq ft??
    I think that rule of thumb only applies in Alaska.

    I would love to see you cool a 5000 sq.ft. home in Houston, Tx. with a 5-ton a/c.
    __________________________________________________ _______________________
    “Experience is a hard teacher because she gives the test first, the lesson afterwards". - Vernon Law

    "Never let success go to your head, and never let failure go to your heart". - Unknown

  5. #5
    Join Date
    Nov 2004
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    SW FL
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    Thumbs down Thumb Sized

    Originally posted by sd47
    ... any thoughts on this??

    Also, rough rule of thumb is given as 1Ton per 1000sq ft??
    This can almost be applied to homes With One 2' x 4' Window + maybe 1 Door__ Along with the ALASKA igloos.
    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

  6. #6
    Join Date
    Mar 2005
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    7
    Apparent I missed the obvious factors like direction of house facing, window area, shade factor, ceiling height, and a lot more, but what I was driving at was more todo with the SEER reduction than anything else??...or maybe I just answered myself...

  7. #7
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    Mar 2005
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    I do appreciate the sarcasm however, although it wasn't particularly conducive to wanting to open my mouth again...lol

  8. #8
    Join Date
    Nov 2004
    Location
    SW FL
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    Equpment Selection

    Originally posted by sd47
    Apparent I missed the obvious factors like direction of house facing, window area, shade factor, ceiling height, and a lot more, but what I was driving at was more todo with the SEER reduction than anything else??...or maybe I just answered myself...
    ...
    1600 Sq. Ft may be well served by
    a 2.5 or 3-ton, high SEER unit
    with Variable Speed Air Handler.
    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
    Mar 2005
    Posts
    7
    I see you're in SWFlorida..so I guess I should have stated that I am in SW Ontario, Canada, where we get temps like 87 with humidex of 94 during our "heat waves"...and normal would be more like 82 with humidex of 88...much the same variance, but easier to live with the second set of numbers, if nothing else...

  10. #10
    Join Date
    Nov 2004
    Location
    SW FL
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    6,432

    Variations

    Originally posted by sd47
    I see you're in SWFlorida..so I guess I should have stated that I am in SW Ontario, Canada, where we get temps like 87 with humidex of 94 during our "heat waves
    So perhaps, Igloos design rule may be Applied.

    There might more than just a slight variation between the
    Artic ( Ontario) and the Tropics (S. FL)

    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

  11. #11
    Join Date
    Mar 2005
    Posts
    7

    Confused

    Assuming the Igloo rule is in effect,,what is the point behind using a 21/2Ton coil with a 2Ton unit??

  12. #12
    Join Date
    Aug 2003
    Posts
    626
    Mrbillpro--If you look at some of the Building America homes by Pulte in Houston you will see about 1 ton per 1000 sq. ft. It's all in the way you build the home.

  13. #13
    Join Date
    Nov 2002
    Location
    VA
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    296
    sd47

    "what is the point behind using a 21/2Ton coil with a 2Ton unit?"

    The same physical coil element is rated at different capacities depending on the refrigerant control device supplying it. What this means is actual coil is a complex factor depending on more variables than mentioned thus far in this thread...

    The only true authority on each unit is the vendor's rep that has to approve the replacement if there is a warranty claim (sad but true). Actually the engineers who design the Coils are totally aware of the performance curves from empirical testing data (which may differ from the original design data).

    HVAC professionals have to go by the numbers and matching units provided be each vendor. There are times when "field modifications" are approved but they are the exception, not the rule.

    What I’m attempting to say is do not focus on capacity numbers, but rather on compliance with the vendors specifications. Does this make sense?

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