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  1. #1
    Join Date
    Apr 2008
    Location
    san pedro,ca
    Posts
    10

    help with system possible ducting.

    Hello I have a 3 ton goodman system. Its cooling aprox 1200 square feet. My contractor has his duct work set up with 2 main branches. The main branch whiches goes to the bedrooms is 12 inch round ducting with another 10 inch branch going to our living room. If we wanted 2 tons of cooling to the bedrooms wouldnt this branch line be to small? I am asking because the unit is not cooling the rooms enought. Thanks for any help you guys can give him. He hasnt been much help.

  2. #2
    Join Date
    Feb 2004
    Location
    chicago suburbs
    Posts
    4,422
    3 tons for 1200 sq'.....typical Gooman install. you are in trouble. find a new contractor.
    FILL OUT YOUR PROFILE!!

  3. #3
    Join Date
    Apr 2008
    Location
    san pedro,ca
    Posts
    10
    Do you think I maybe undersized? I had 5 bids 3 out of 5 told me a 3 ton system. Only one said 4 ton the other said 2.5 ton. So I dont know who to call.

  4. #4
    Join Date
    Jan 2004
    Location
    PA
    Posts
    68,770
    What area do you live in.

    Its sounds more like the unit is oversized.
    And the duct is undersized.
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    How many times must one fix something before it is fixed?

  5. #5
    Join Date
    Feb 2004
    Location
    chicago suburbs
    Posts
    4,422
    duct is close....unit is too big unless you leave you windows open all summer or you live on the sun.

    take 2 seconds and fill out your profile.
    FILL OUT YOUR PROFILE!!

  6. #6
    Join Date
    Apr 2008
    Location
    san pedro,ca
    Posts
    10
    Thats good because I would rather be oversized than undersized. I live in california in the los angeles area. The house has an open beam ceiling so most the installers suggested 3 tons because of this. The orginal installer wants to upgrade me to a 4 ton system. So I am confused one of my friends works in the ac field but does commerical installs only (union work) but he told me that is not the correct size for my install is this true?

  7. #7
    Join Date
    Mar 2004
    Location
    Illinois
    Posts
    6,959
    Quote Originally Posted by tinner73 View Post
    duct is close....unit is too big unless you leave you windows open all summer or you live on the sun.

    take 2 seconds and fill out your profile.
    Let's assume for a moment he lives in Arizona?

  8. #8
    Join Date
    Feb 2004
    Location
    chicago suburbs
    Posts
    4,422
    the union guy is right (go figure) too big is not good,


    get a load calc above.
    FILL OUT YOUR PROFILE!!

  9. #9
    Join Date
    Jan 2004
    Location
    PA
    Posts
    68,770
    They should have done a load calc. Then they would know what size you really needed instead of guessing.

    Here, you can do your own.
    http://hvaccomputer.com/talkref.asp

    Your duct is too small for 3 tons. You would need all new duct work.

    The current 3 ton may not cool just because of the undersized duct work.
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    How many times must one fix something before it is fixed?

  10. #10
    Join Date
    Apr 2008
    Location
    san pedro,ca
    Posts
    10
    Yeah the unit runs constantly never shuts down and can not cool the house down past 79 degrees with the windows all closed. I highly doubt a smaller unit would do the trick this almost makes me wish I would have stuck to my window ac units than going with central. What can I do now though the installer is saying I need to go bigger not on my ducts but system tonnage.

  11. #11
    Join Date
    Feb 2004
    Location
    chicago suburbs
    Posts
    4,422
    2tons = 800cfm @ 1000fpm = 12"round
    1 ton = 400cfm @ 1000fpm = 8.5"round

    ductulator in hand

    duct is good for metal.
    Last edited by tinner73; 09-01-2008 at 09:45 PM.
    FILL OUT YOUR PROFILE!!

  12. #12
    Join Date
    Feb 2004
    Location
    chicago suburbs
    Posts
    4,422
    do you have flex duct??
    FILL OUT YOUR PROFILE!!

  13. #13
    Join Date
    Jan 2004
    Location
    PA
    Posts
    68,770
    Your duct system could have air leaks. I would check for leaks before investing money in a larger system. And replacing the duct work.

    Use the link and do your own load calc if you can't find a contractor to do one.
    Contractor locator map

    How-to-apply-for-Professional

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

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