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  1. #1
    Installer says that all round ductwork has a better airflow than the existing square one and he will install all round ductwork - is this right?

  2. #2
    Join Date
    Apr 2003
    Location
    Iowa
    Posts
    763
    depends on what size you have.... usually to get best air flow you have a square trunk line with round pipe coming off it....
    a six inch round pipe is around 100 cfm 105
    a seven inch is around 150
    8 230
    square is 12x8 around 500
    14 x 8 is 600 etc etc etc...
    your furnace has a 3 ton blower or 4 or what ever
    1 ton equals 400 cfm..... so 3 ton is 1200 etc.
    make sure you have enough air innnnnn and enough air outttttt so you don't have heat exchanger problems early in system....

  3. #3
    Join Date
    Jul 2000
    Location
    DeFuniak Springs, FL
    Posts
    990

    Yes

    If all the design parameters are correct.
    Randy Yates

  4. #4
    Join Date
    Oct 2001
    Location
    Waterford Michigan
    Posts
    2,668

  5. #5
    Join Date
    Oct 2001
    Location
    Waterford Michigan
    Posts
    2,668
    One common practice is rectangular trunks with round run-outs. Proper sizing is more important than round or square.

  6. #6
    Join Date
    Jan 2001
    Posts
    7,904
    a properly sized round duct system will deliver the air more efficiently than a square or rectangular system....even with rectangular duct...the closer you get the two dimensions closer to a square shape the better the airflow through the duct. round is best because the air moving thru it exerts an equal pressure along the interior of the ducting and this results in smoother more efficient airflow.

    The biggest reason people are going to round now is that it is easier to install and cheaper as it actually takes less metal than square or rectangular equivalents. But its better for you the consumer because you are pretty well assured of getting a better sealed system with round pipe...Ive seen countless rectangular duct systems with leaks you could stick your hand thru where the installer couldnt get the duct connected properly and just gave up and taped over the gaping hole left where the connector goes.....tape eventually works loose and you have a massive air leak.

    I once tore out a whole system where the installers just jammed the rectangular duct together without using the S lock and drive cleat connectors...it was jammed together and the joints taped....when the system would come on the insulation around the duct would balloon out...the original installers were not fly by nights either...they had been doing business for some time and still are today.


  7. #7
    Join Date
    Nov 2000
    Location
    Waco, Texas, USA
    Posts
    6,153
    Good post corny .......but what about noise issues?
    "And remember my sentimental friend......that a heart is not judged by how much you love, but by how much you are loved by others" - Wizard of Oz.

  8. #8
    Join Date
    Nov 2004
    Location
    Thibodaux, LA
    Posts
    1,170

    Re: Yes

    Originally posted by heatpumpman
    If all the design parameters are correct.
    Square or round?

    ROUND YES

    Exactly

  9. #9
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    A round duct system is no more efficient than a square one ,with comparable design,same goes for flex duct.

    Round will consume less sheet metal to get the same airflow,but that doesn't mean it will be more efficient.Same goes for sq. versus rectangular,rectangular wil consume more metal for the same airflow.

    There is one small advantage,since it takes less sheet metal to handle the same airflow,it takes less insulation,so the end result will have slightly less duct loss,due to temperature difference.

  10. #10
    Join Date
    Sep 2002
    Posts
    4,970
    [QUOTE]Originally posted by dash
    [B]A round duct system is no more efficient than a square one ,with comparable design,same goes for flex duct.

    QUOTE]

    Well I may be wrong but I was always under the impression that round if sized right and of same material (flex would be differant) would have better air flow characteristics then square or rectangle. That being that with the square corners ,that would cause more friction , turblence and tumbling of the airflow as compared to round. I may be wrong but it always made sense to me . In my opinion more square is better then retangular but round is better then square.

  11. #11
    I've been told I'm a good tester (testing person). Whatever I stumble on or use I find unusual problems, bugs or questions. So there comes another one for this forum:

    How about a TRIANGULAR duct vs. SQUARE duct?
    Also: OVAL vs. ROUND.

    :-)

  12. #12
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    12" round,10"X11",and 21"X6",all have the same airflow characteristics ,except velociy which will be less in the 10X11 and even less in the 21X6,assuming the same material.Check your ductolator,to verify.

  13. #13
    Join Date
    Sep 2002
    Posts
    4,970
    hummmm .... I have no idea how to go about making triangular offsets and elbows. I think I will stay away from the triangular conversation in that case. Altho I have seen a little triangular duct run down trusses but when it came to the connections where it adapted to the round or rectangular duct ,it wasnt any connection that would create good air flow.

    [Edited by dec on 01-29-2005 at 02:45 PM]

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