Results 1 to 7 of 7
  1. #1
    Join Date
    Jul 2003
    Posts
    32

    What is a good rule of thumb regarding duct velocity?

    What is the recommended velocity range (feet per minute) to keep airflow noise to a minimum? (Using flex duct in a residential application).

    Thanks Guys!

  2. #2
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304
    ACCA Manual D clearly says 600 feet/min is recommended and 700 fpm max. This is not a rule of thumb but formal ACCA training. I believe duct noise will not be great if you follow this. My own experience is that upon changing an air handler, I once got approximately 860 fpm from one duct, and you could hear the "freight train" noise pretty plainly.

    That was with the air handler set for 1400 cfm total, on a 3.5 ton AC. When I reduced air flow to 1200 cfm, the noise was much reduced -- I figure the new air speed is 730-740 fpm.

    Hope this helps -- Pstu

  3. #3
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    900 fpm in trunks and 600 fpm in branch ducts.

    Manual D for flex is based on the original flex,not todays flex.

  4. #4
    Join Date
    Apr 2002
    Posts
    11,808
    Those numbers sound good to me dash
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  5. #5
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304
    So flex duct is a product which has changed since Manual D was written? I would be interested in knowing more, if you could tell me. I am starting at square one on this matter.

    Thanks -- Pstu

  6. #6
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Early flex had like 3" wide strips ,that weren't sealed well to each other ,wraped around the helix wire coil.So at higher velocities they "flaped' and made noise.

    Todays flex doesn't ,Manual D will be revised soon ,and that will likely be one change.

  7. #7
    Join Date
    Apr 2005
    Location
    Tampa, Florida
    Posts
    1,634
    For comparison, we use a figure of 250ft/min maximum for recording / television studio applications... As you can imagine, we oversize everything to achieve these levels. Very simple to do in a commercial studio, but chances are you're not going to have enough room in the average home to do it. Still, lower fpm will give you a quieter system.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event