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  1. #1
    Join Date
    Feb 2013
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    Replacing flex duct

    Need my 27 yr old gray flex duct replaced. Have two quotes. Would like some advice on which company to use.

    Small company - came recommended from a friend, didn't leave a paper copy of the quote, quoted R6, very good price. Not leaving a quote and quoting R6 raises some red flags for me. Am I just being too critical? I do like the price.

    Large company - left detailed paper copy quote, R8, want to move return registers to top of walls, cost is double the smaller company. Like the detail of the large company but do the returns registers need to be moved? Overkill? The HVAC system has worked good for the 10 yrs I've been in the house. The bills are not too high. 2000 sq ft house.

    Thanks,

  2. #2
    Join Date
    Dec 2005
    Location
    Cincinnati, Oh
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    attic or crawl?

    Any warranties?
    No quote leads me to be weary.
    "Better tell the sandman to stay away, because we're gonna be workin on this one all night."

    "Dude, you need more than 2 wires to a condenser to run a 2 stage heatpump."

    "Just get it done son."

    Dad adjusted

  3. #3
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,471
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    I would press the larger company to explain why they want to move the return grills up. Could be your existing returns use building cavities, and they want to get you away from that by going straight from the return to the duct. If that's true, that's a good thing.

    The replacement flex duct should NOT have a black jacket on it. It should be a "foil" like jacket, which can withstand high attic temperatures. You definitely want R8. All flex duct must be stretched tight, suspended with webbing at least 1 1/2" wide, and mastic sealed and mechanically banded at ALL connections. No kinks should be in the duct anywhere, and they really should use a metal 90 elbow instead of trying to make the flex duct turn 90 degrees. These practices are bare minimum to ensuring the replacement flex duct performs better than your existing flex duct.

    I would want all of this called out on any bid I might consider.
    Building Physics Rule #1: Hot flows to cold.


    Building Physics Rule #2:
    Higher air pressure moves toward lower air pressure


    Building Physics Rule #3:
    Higher moisture concentration moves toward lower moisture concentration.

  4. #4
    Join Date
    Dec 2005
    Location
    Cincinnati, Oh
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    Quote Originally Posted by Shophound View Post
    I would press the larger company to explain why they want to move the return grills up. Could be your existing returns use building cavities, and they want to get you away from that by going straight from the return to the duct. If that's true, that's a good thing.

    The replacement flex duct should NOT have a black jacket on it. It should be a "foil" like jacket, which can withstand high attic temperatures. You definitely want R8. All flex duct must be stretched tight, suspended with webbing at least 1 1/2" wide, and mastic sealed and mechanically banded at ALL connections. No kinks should be in the duct anywhere, and they really should use a metal 90 elbow instead of trying to make the flex duct turn 90 degrees. These practices are bare minimum to ensuring the replacement flex duct performs better than your existing flex duct.

    I would want all of this called out on any bid I might consider.
    Unless it's in a crawl space.

    Then you don't want flex at all. All wrapped metal.
    "Better tell the sandman to stay away, because we're gonna be workin on this one all night."

    "Dude, you need more than 2 wires to a condenser to run a 2 stage heatpump."

    "Just get it done son."

    Dad adjusted

  5. #5
    Join Date
    May 2004
    Location
    south louisiana
    Posts
    3,579
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    Quote Originally Posted by Shophound View Post
    I would press the larger company to explain why they want to move the return grills up. Could be your existing returns use building cavities, and they want to get you away from that by going straight from the return to the duct. If that's true, that's a good thing.

    The replacement flex duct should NOT have a black jacket on it. It should be a "foil" like jacket, which can withstand high attic temperatures. You definitely want R8. All flex duct must be stretched tight, suspended with webbing at least 1 1/2" wide, and mastic sealed and mechanically banded at ALL connections. No kinks should be in the duct anywhere, and they really should use a metal 90 elbow instead of trying to make the flex duct turn 90 degrees. These practices are bare minimum to ensuring the replacement flex duct performs better than your existing flex duct.

    I would want all of this called out on any bid I might consider.
    x2. I like 3" duct strapping. no more than 1" sag in 4' length. 90's at supply
    boxes is great.

    can you take a picture inside the return?

    no foil or duct tapes, mastic and mastic tape only.
    have them check inside supply plenum when old ducts are removed.
    when ducts are not sealed properly the supply plenum can get pretty nasty.
    wouldn't want any thing from plenum to get into new ducts.
    option to replace supply plenum if necessary.


    have them address any hot/cold areas and any concerns you have
    while on the job. try to be around during the day to see what is
    going on. I usually keep the ducts I take out on the site for the day
    before removing them, so that home owner sees why they were replaced.


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

  6. #6
    Join Date
    Feb 2013
    Posts
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    Thanks for the replies. The ducts are in the attic and I think you are right, Shophound, about the cavities. That sounds familiar.

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