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  1. #1

    Too much ductwork?

    Hello! We have a 2300 sq ft modular home. We had a 4-ton unit installed in May of last year. Where we live in the SE US, it commonly gets up to 100, occasionally up to 110 degrees in summer. Our air conditioner was running from around 11am until 6pm without stopping, with the air in the house getting to 77 degrees on an 89 degree day. The people who installed the unit checked it about a dozen times, couldn't find any problem, so told us we needed a 5-ton, 15 seer unit. This was installed about a month ago. We have had a VERY mild summer this year, but the air inside is still getting to 77 on a 90 degree day. We keep the curtains closed and have some shade on our home in the mornings.

    Under the house, there appears to be about 30' of 14" flex pipe just pretzelled around (out of a total of about 50' under the house), twisting and turning under other pipes. We have mentioned this to the installers but they won't even look at it and insist they can't find a problem. It seems to me having to push the air through all this excess pipe through all the extra twists and turns is only making it work harder, but I don't claim to know a darn thing about air conditioning systems or ductwork! Could too much pipe cause this type of problem?

    We have a 14" supply and 14" return going to the package unit. We have two returns with 14" flex pipe, tied together to a 14" flex, then it goes to the unit. My electric bill runs around $400 a month in summer and our lowest bill was in October at $159. The summer bills kill me

    Any advice is much appreciated!!

  2. #2
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    5,031
    Could too much pipe cause this type of problem?
    Yes, that certainly can be a major part of the problem.
    Why is you can see the problem & the so-called HVAC guys can't!

    That system is simply NOT Performing...

    It takes a great lot of both supply & return for 4 & 5-Ton systems; plus two (2) very large Return Air Filter areas.

    The major problem, as it appears from here, is the install & a very poor duct system; how many supply air registers does it have & what size are the flex duct runs. Flex duct has to be short runs stretched tight with metal or hard type turns; take a photo of that mess & upload it.

    Here is a Free Online Whole House load-calc you can print the instructions & follow them to the letter for a 'possible' ballpark on what size equipment is required.

    However, it has to be matched with a duct system that allows it to get 85 to 90% delivered performance, -of its Btuh Rating. The duct system has to be corrected using Manual D, & its STANDARDS!


    .

  3. #3
    Join Date
    Jan 2004
    Location
    PA
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    68,763
    A 14" flex isn't big enough for a 4 ton unit. So it is no where close to big enough for a 5 ton. Your undersized return and supply are most likely the reason that the 4 ton couldn't cool your house right.

    14" is what is often used on 2.5 and 3 ton package units on modular and MHs. not on 4 or 5 ton units.
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  4. #4
    Wow, you guys are truly awesome!!!

    We have two returns and 15 registers. There is one register in each bathroom (2 bathrooms) and bedroom (4 bedrooms), three registers in the living room, three in the playroom, two in the dining room, one in the kitchen. I can't get under the house tonight to take a picture of the mess, but I was able to read your posts a few minutes before the installer got here a little over an hour ago, so my husband had this little arsenal of information from you guys!! The installer looked at the mess under the house, which we've been asking them to do for months, and said they are going to pull out the 14" and put in 16" for the supply and return up to the Ys. I'm hoping this will help keep it cooler in here and help the electric bill come down a bit. I'll update after the work is done and let you guys know how it's going.

    Thank you SO, so much for taking the time to reply to my post!! I sincerely appreciate it!

  5. #5
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
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    2,744
    Quote Originally Posted by Roses View Post
    Wow, you guys are truly awesome!!!

    We have two returns and 15 registers. There is one register in each bathroom (2 bathrooms) and bedroom (4 bedrooms), three registers in the living room, three in the playroom, two in the dining room, one in the kitchen. I can't get under the house tonight to take a picture of the mess, but I was able to read your posts a few minutes before the installer got here a little over an hour ago, so my husband had this little arsenal of information from you guys!! The installer looked at the mess under the house, which we've been asking them to do for months, and said they are going to pull out the 14" and put in 16" for the supply and return up to the Ys. I'm hoping this will help keep it cooler in here and help the electric bill come down a bit. I'll update after the work is done and let you guys know how it's going.

    Thank you SO, so much for taking the time to reply to my post!! I sincerely appreciate it!
    You should ask them to run 20" flex (not 16") to the tees and run the 14" flex off of that. The 14" flex off the unit was the problem all along.

  6. #6
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    5,031
    Quote Originally Posted by George2 View Post
    You should ask them to run 20" flex (not 16") to the tees and run the 14" flex off of that. The 14" flex off the unit was the problem all along.
    Pay attention to what George2 is telling you or, the main run will be too small for 5-Ton...
    Operate the blower at 350-CFM per ton of cooling or slightly less; 1750-CFM or a little less.

  7. #7
    Join Date
    Jul 2006
    Location
    Virginia
    Posts
    4,873
    time to replace the contractor
    We really need change now

  8. #8
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,428
    A MINIMUM OF TWO 16" Diameter DUCTS IS REQUIRED.
    I assume many would prefer 18".

    FLEX DUCT MUST BE FULLY EXTENDED.
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  9. #9
    Join Date
    May 2004
    Location
    south louisiana
    Posts
    3,318
    while they are changing the flex for the return...they
    should also mastic seal all the ducts, supply boxes, plenums
    & plenums to equipment.
    flex should also be strapped with duct straps (3" duct straps
    every 4') to keep it off ground, and eliminate any bends
    or restrictions.

    difficult to get hvac company to do this...as you can see by
    having to point out at least twice your ductwork concerns.

    best of luck.
    The cure of the part should not be attempted without the cure of the whole. ~Plato

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