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  1. #1
    Join Date
    Aug 2013
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    24

    Return run....trimming excess flex from run

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    Hopefully there are three pictures shown here. They show a 14" return flex line that I think has excess line in it, and can be redone to reduce the flex amount. I am having my compressor replaced on Monday, so I have been tossing around the idea to have them fix this if necessary. What I would like them to do is place a 90 degree elbow where it comes thru the wall, should be picture 1 into 2, and then run the flex along the wall to the return box, adding a 90 degree elbow into the box to prevent kinks there. By adding the elbows and stretching the flex between the two elbows along the wall, that should eliminate several feet of 14" duct. That would be very beneficial, correct, with the return air in this line??? Or is it better having lots of 14" line snaking around the attic?

    Just in case the pictures don't show, the line comes thru the attic, makes almost a 90 degree turn to parallel the ceiling, goes thru a wall, and then takes a very gracious lazy 90 degree turn, not bending the flex duct, and back to the return box, which is almost against the opposite side of the wall that it penetrates the first time. So it is a big lazy S, and not a tighter S that could be there with the 90 degree elbows. Make sense?

  2. #2
    Join Date
    Jul 2006
    Posts
    1,091
    Shorter and less turns the better. You might want to make sure the return air grille and return air duct is the correct size for your equipment while you're at it.

  3. #3
    Join Date
    Aug 2013
    Posts
    24
    Quote Originally Posted by rickboggs View Post
    Shorter and less turns the better. You might want to make sure the return air grille and return air duct is the correct size for your equipment while you're at it.
    I checked the air filter yesterday, and looked inside the return trunk. This flex duct in question was really bunched up on the inside of this 90 degree turn, I would say blocking around 20% of the opening. I am going to insist that this change be made.

    Thanks.

  4. #4
    Join Date
    Jul 2006
    Posts
    1,091
    Quote Originally Posted by Gritbob View Post
    I checked the air filter yesterday, and looked inside the return trunk. This flex duct in question was really bunched up on the inside of this 90 degree turn, I would say blocking around 20% of the opening. I am going to insist that this change be made.

    Thanks.
    What size is your equipment?
    What size is you filter?
    Is the duct the right size?

    If they're not the right size for your equipment and you're just gonna leave it, I would waste my money straightening out the bends.

  5. #5
    Join Date
    Aug 2013
    Posts
    24
    Quote Originally Posted by rickboggs View Post
    What size is your equipment?
    What size is you filter?
    Is the duct the right size?

    If they're not the right size for your equipment and you're just gonna leave it, I would waste my money straightening out the bends.
    2.5 ton system
    filter is 20x25x4
    Return ducts are 14", 14", 10" flex duct

    My system is almost balanced. Appears to have had leakage in the return duct lines based on the air flow readings. They have been sealed up now (not verified by air flow readings yet.) This line had lower return flow than the other 14" line (both have the same sized grill openings) so I was concerned about the lower flow in this return. By removing the excess flex line (I am guessing it will total several feet removed), stretching it tight, and adding the 90 degree elbows, it will maximize its return airflow, and thus fully balance the system.

  6. #6
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,327
    What is with all the pics I've been seeing lately here on AOP of black lined flex running through scorching hot attics? Are some installers merely averse to using reflective mylar jacketed flex?

    The "wall" that is in the attic...is it merely to separate one section of the attic from another? Reason I ask is I don't see any insulation on the wall where the black flex passes through. If it does not adjoin living space, no big deal.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  7. #7
    Join Date
    Aug 2013
    Posts
    24
    Quote Originally Posted by Shophound View Post
    What is with all the pics I've been seeing lately here on AOP of black lined flex running through scorching hot attics? Are some installers merely averse to using reflective mylar jacketed flex?

    The "wall" that is in the attic...is it merely to separate one section of the attic from another? Reason I ask is I don't see any insulation on the wall where the black flex passes through. If it does not adjoin living space, no big deal.
    Yes, it merely separates two parts of the attic.

  8. #8
    Join Date
    May 2004
    Location
    south louisiana
    Posts
    3,170
    shophound, it does make one wonder where all the black flex is comming from.
    I rarely see black flex these days.

    OP you shouldn't have exposed insulation at the ends of the flex.
    it should be fitted to stay in contact with the ductboard plenum
    with black (...) vapor barrier of duct sealed to foil of ductboard.
    on the other end it should be trimmed, tucked inside vapor
    barrie liner & sealed to the connection there.

    straight tight runs move air better.
    in my hot humid climate we strap ducts off insulation because it
    condensates where it touches the insulation.
    in dryer climates it is ok for it to lie on insulation.

    what is your location?

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

  9. #9
    Join Date
    Aug 2013
    Posts
    24
    Quote Originally Posted by energy_rater_La View Post
    shophound, it does make one wonder where all the black flex is comming from.
    I rarely see black flex these days.

    OP you shouldn't have exposed insulation at the ends of the flex.
    it should be fitted to stay in contact with the ductboard plenum
    with black (...) vapor barrier of duct sealed to foil of ductboard.
    on the other end it should be trimmed, tucked inside vapor
    barrie liner & sealed to the connection there.

    straight tight runs move air better.
    in my hot humid climate we strap ducts off insulation because it
    condensates where it touches the insulation.
    in dryer climates it is ok for it to lie on insulation.

    what is your location?

    best of luck.
    Eastern PA

  10. #10
    Join Date
    Jun 2011
    Location
    Central Indiana
    Posts
    615
    I see black flex all the time. Heck, I work in a lot of tract homes and most of it is R-4. We install mylar jacketed flex but the guys at the supply shop think we are crazy for it. They always tell me we are the only ones who buy it.

    The more strait the run the better. But without seeing the attic, it is hard to tell. Its possible the flex is run this way to prevent tight pinching turns, but this can probably be solved by installed properly insulated metal pipe 90s. But at the same time, putting a bunch of 90s in will not make it much better.

    From my computer screen, it looks like that run could use a little attention, but at the same time I have seen much worse.
    The only true knowledge is the pursuit of knowledge

  11. #11
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    6,844
    The only places I see black jacketed flex duct around here is on the connector duct on double/triple wide mobile homes. The duct doesn't look that bad to me from what I can see, I've seen lots worse. The vapor barrier should be continuous.

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