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  1. #1
    Join Date
    Nov 2006
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    13

    Confused Question-mark curves in ductwork

    We've just had a partial reducting done to get rid of some through-slab ductwork that had become a breeding ground for mold. The installer put a number of question-mark like curves in the new ductwork. What are these curves for?







    I'm assuming there's a good reason for doing this--after all it's more work than running a straight section of duct--but I'm scratching my head as to why it was done this way.

  2. #2
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,914
    It is funny looking, and isn't the least restrictive way it could have been done.
    If the ducts are sized to account for all those fittings, it isn't an issue, but that sure is a lot of fittings, lol.

    One issue I have with it is that they sealed all the duct connections with mastic, but didn't seal the joints in the elbows. Unsealed elbows leak, often worse than unsealed duct connections...
    If more government is the answer, then it's a really stupid question.

  3. #3
    Join Date
    Jun 2007
    Location
    Metro St. Louis
    Posts
    181
    The pipe on the left looks like your trunk run. By doing it this way, he's attempting to keep the branch runs somewhat even. If he had gone strait thru, you would see more airflow out of that duct in comparison to the others.

    Basically, he's trying to keep the effective length of the ducts similar.

  4. #4
    Join Date
    Jan 2004
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    Here and there
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    Not seeing the whole system it's hard to tell. The fact they sealed the joints tells me at least they care about quality. Waterloo, do you know a feller named Chuck ?
    i belong to peta ... people eating tasty animals. all my opinions are just mine.

  5. #5
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    No way is that right.

  6. #6
    Join Date
    Sep 2005
    Location
    Texas
    Posts
    2,793

    wouldn't dampers...

    ...do the same thing? I also believe those ducts need to be suspended.



    Quote Originally Posted by Waterloo View Post
    The pipe on the left looks like your trunk run. By doing it this way, he's attempting to keep the branch runs somewhat even. If he had gone strait thru, you would see more airflow out of that duct in comparison to the others.

    Basically, he's trying to keep the effective length of the ducts similar.

  7. #7
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,914
    Quote Originally Posted by jpb2 View Post
    Not seeing the whole system it's hard to tell. The fact they sealed the joints tells me at least they care about quality.
    They didn't seal the joints in the elbows though...
    If more government is the answer, then it's a really stupid question.

  8. #8
    Join Date
    Nov 2006
    Posts
    13
    My first guess was for flow reduction as there are no dampers anywhere in the system. Second guess is for noise attenuation, however there are already two 90 degree bends between the air handler and trunk.

    I will ask the installer.

  9. #9
    Join Date
    Jun 2007
    Location
    Metro St. Louis
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    181
    Quote Originally Posted by jpb2 View Post
    Not seeing the whole system it's hard to tell. The fact they sealed the joints tells me at least they care about quality. Waterloo, do you know a feller named Chuck ?
    I know two Chucks. One's an uncle in IA. The other is my boss.

    Don't know anyone in the HVAC world by the name of Chuck.

  10. #10
    Join Date
    Apr 2004
    Posts
    7,680
    At least they understand that supply runs should not be taken off the ends of the main trunk. It may look goofy, but outside of the mastic missing from the seams in the ells, I wouldnt wory to much about it. At least they didnt run flex.

  11. #11
    Join Date
    Jan 2004
    Location
    Here and there
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    Quote Originally Posted by Waterloo View Post
    I know two Chucks. One's an uncle in IA. The other is my boss.

    Don't know anyone in the HVAC world by the name of Chuck.
    Don Heck or Chuck Meadgee ? just a thought.
    i belong to peta ... people eating tasty animals. all my opinions are just mine.

  12. #12
    Join Date
    Nov 2007
    Location
    Chicago
    Posts
    76
    Quote Originally Posted by docholiday View Post
    At least they understand that supply runs should not be taken off the ends of the main trunk. It may look goofy, but outside of the mastic missing from the seams in the ells, I wouldnt wory to much about it. At least they didnt run flex.
    Why not run flex if they are just going to install it like that??

    You've got 3 90deg elbows right next to each other and no dampers. That is a huge static pressure drop. Unless the rest of the system is balanced properly [and you mentioned no dampers] there will be little to no airflow through that.

  13. #13
    Join Date
    Apr 2004
    Posts
    7,680
    Imagine the inside of a flex with those curves... for a 6" run 10 feet long you'd be lucky to get 50 cfm at the right static and velocity. rounded ells, dont cause that much restriction. Coming off the end would have made a mess of the entire system static.

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