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  1. #1
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    Need some advice for a poorly working CAC

    I have a brand new CAC installed in April, that hasnt been cooling properly, and just recently started leaking moisture into the secondary pan. It is a TRANE 5ton unit with Matching VS Blower Air handler. The ducting is all new, using flex. I will have installer at house 1 last time to try and properly get the unit working properly. I believe most of my issues are the ducting is way undersized. I have 1 18" return in the main hallway of the 1st floor, and 1 10" return in the hallway of the 2nd floor. I then have a total of 10 7" and 2 6"supplies. My house is a 1960 Farm ranch with r11 insulation in walls, but newly installed r40 blown in in the attic. The unit is noisy as hell, especially the 18" return. I am having issues keeping the 2nd floor cool. It has 3 7" supply feeding each bedroom, and a 6" in the hallway. Downstairs cools fine. I attached a few pics of the AH. On the right is the return with the 2 flex hookups. This to me looks WAY undersized to feed 2000cfm. What are my options? This will be his last chance before I hire another contractor. Please give some thoughts. Thanks

    By yamvmax at 2012-08-10

    By yamvmax at 2012-08-10

  2. #2
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    5 tons.
    That's the problem.
    "Hey Lama, hey, how about a little something, you know, for the effort." And he says, "there won't be any money, but when you die, on your deathbed, you will receive total consciousness." So I got that goin' for me, which is nice. - Carl Spackler

  3. #3
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    Quote Originally Posted by 2old2rock View Post
    5 tons.
    That's the problem.
    ???????????? So what exactly does that mean?

  4. #4
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    7" flex, that's about 125 CFM each or 1250.
    6" flex, say 80 CFM or 160.
    1410 CFM worth of supply. A 3.5 ton would like that.
    18" & 10" flex on the return is better. But if noisy, something not right.

    How did he arrive at 5 tons for the house? NYC isn't south Florida or Phoenix. We size to 95 out and the typical 2000 sq ft would be 2.5 ton, 3 ton max. Probably 2.5 ton with the good insulation you have. Given the duct system you have, 2.5 or 3 ton would be about right and quiet too.

  5. #5
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    The second floor is 1200sq feet, and sort of like a cape, so the solar/heat gain up there is tremendous. He did jcalc..or whatever you guys call it. Many windows, and NO shade. My thoughts are change the 7" supplies upstairs to 8"? Its the upstairs that is having issues cooling. EDIT>>>>>>> The 18" isnst 18, its 16".

  6. #6
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    Quote Originally Posted by suzook View Post
    The second floor is 1200sq feet, and sort of like a cape, so the solar/heat gain up there is tremendous. He did jcalc..or whatever you guys call it. Many windows, and NO shade. My thoughts are change the 7" supplies upstairs to 8"? Its the upstairs that is having issues cooling. EDIT>>>>>>> The 18" isnst 18, its 16".
    Yeah, that 18 to 16 changed the ball game on your return. Shy.

    Undersized duct system.

    Was this inspected?
    "Better tell the sandman to stay away, because we're gonna be workin on this one all night."

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  7. #7
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    No, not inspected. Should I try and convince him to change that 16 to an 18, maybe the 10 to a 12? That should give me about 2000cfm...no?

  8. #8
    Join Date
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    Wow. 5 ton is grossly oversized. We just took a guys 5 ton unit of his house that was only 3 years old. We put in a 3 1/2 ton unit and he has never been more comfortable. Sounds like to me it wasn't designed properly

  9. #9
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    Quote Originally Posted by suzook View Post
    No, not inspected. Should I try and convince him to change that 16 to an 18, maybe the 10 to a 12? That should give me about 2000cfm...no?
    That will give you the 2000 for return. What is the dimension of the supply trunk?

    It looks quite small

  10. #10
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    Leave the 16" return alone, as far as its size. Have him increase the return for the second floor to 16" also. Which means he'll need to increase the return grille size also. Your return plenum is short so just making the 10" a 16" won't get you the full flow because of the turbulence that will be caused in the plenum. Increasing the supply size to the upstairs rooms will also help. but as the others have said, 5 tons sounds over size for your little place.
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  11. #11
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    Quote Originally Posted by second opinion View Post
    That will give you the 2000 for return. What is the dimension of the supply trunk?

    It looks quite small
    The pic is not great, its about 20 feet long.


    Quote Originally Posted by beenthere View Post
    Leave the 16" return alone, as far as its size. Have him increase the return for the second floor to 16" also. Which means he'll need to increase the return grille size also. Your return plenum is short so just making the 10" a 16" won't get you the full flow because of the turbulence that will be caused in the plenum. Increasing the supply size to the upstairs rooms will also help. but as the others have said, 5 tons sounds over size for your little place.
    I had 3 estimates done, all with manual j done. All came up with 5ton. As many here are pointing out, lets say its oversized. Being that its oversized, my place should be an icebox and clamy. Well its not. Its on the warm side upstairs where most of the heat load is. So I should suggest bigger return AND supply upstairs? And a biggger return plenum? Thanks for the suggestions, I just want to get this working as well as I can.

  12. #12
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    jpsmith1cm is offline Global Moderator/AOP Committee
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    Quote Originally Posted by Bsmith816 View Post
    Wow. 5 ton is grossly oversized. We just took a guys 5 ton unit of his house that was only 3 years old. We put in a 3 1/2 ton unit and he has never been more comfortable. Sounds like to me it wasn't designed properly
    Bsmith816

    Please check your PMs.

  13. #13
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    Quote Originally Posted by suzook View Post
    The pic is not great, its about 20 feet long.




    I had 3 estimates done, all with manual j done. All came up with 5ton. As many here are pointing out, lets say its oversized. Being that its oversized, my place should be an icebox and clamy. Well its not. Its on the warm side upstairs where most of the heat load is. So I should suggest bigger return AND supply upstairs? And a biggger return plenum? Thanks for the suggestions, I just want to get this working as well as I can.
    One of the reasons your upstairs is warm is because its over sized. it doesn't get to run long enough to cool the upstairs where the heat load is. Having under sized duct work also decreases the capacity of the unit. Increasing return size and supply size will help. But it will still be over sized.

    Did the contractor leave the load calc with you.
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