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Thread: duct fittings

  1. #1
    Join Date
    Apr 2005
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    illinois
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    257
    Are there fittings that are more efficient when making the transition from the branch duct to the floor register? I saw a web article that referred to this but there was not much detail. Talked about a 3 seam elbow versus a 90 degree mitered connection. Seemed that some fittings are quite inefficient. Is flex duct a bad idea to use as a boot? Are there fittings that leak less? I am having the ducts redone and want to be able to suggest to my contractor the most efficient fitting.
    Does anybody have any experience with tapered fittings to start a branch run?

    [Edited by heetseeker on 06-04-2005 at 03:58 PM]

  2. #2
    Join Date
    May 2004
    Location
    Illinois
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    2,843
    Find a copy of either the ASHRAE Fundamentals handbook, or the SMACNA Duct design. Your local library should be able to get them for you, if they don't have it in stock.

    Both those books have tabulated pressure drop data for every kind of fitting you can imagine.

  3. #3
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
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    18,836
    There is a difference in various fittings .With branch fitting ,it's not a major factor.Most branchs have two or three fitting,so if you save 15 equivalent feet on each branch,it sounds like a lot,however the "longest run,includin its branch is the only one the counts.So it may not be worth the money.

  4. #4
    Join Date
    Apr 2005
    Location
    illinois
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    257
    Dash
    I am redoing the 2 [ about 24 ft each ]longest branches at the end of one of the main trunks so I am trying to preserve airflow as much as possible. Is there any special type of register boot or fitting that is significantly better for air flow? These have been a problem in the past. I found that the ducts were disconnected. Now I would like them fixed as well as possible.

  5. #5
    Join Date
    Jul 2004
    Location
    Kent, WA
    Posts
    129
    In the back of Manual D, they list the effective lengths for many duct fittings. The type 4-G is what I've seen in most houses for a round to rectangular register boot (and the register is perpendicular to the round pipe).

    There is a different style 4-K that drops the effective length from 80' of the 4-G to 30'. They best way to describe the difference of this type of fitting is instead of the round duct transitioning into a rectangular opening pointing up, the rectangular portion is straight in line with the round pipe. Then there is a longer radius rectangle 90 bend to get the rectangle pointing up.

    Will 50 feet make up enough of a difference?

  6. #6
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    Apr 2005
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    illinois
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    Thanks Do you know where there mught be a supplier or some sort of picture of the 4-k.

  7. #7
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
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    Most sheet metal or HVAC supply houses in your area,should be able to get them.Note the "radius" difference of 4K and 4L,to get the right one.

    4-R with an elbow may be easier to find and would be an improvement.



  8. #8
    Join Date
    Apr 2005
    Location
    illinois
    Posts
    257
    I have tried to find the more efficient boots both online and locally without any success. Can anyone give me a clue about how to find the supply boots mentioned in the two posts above?

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