Results 1 to 7 of 7

Thread: duct sizing

  1. #1
    Join Date
    Sep 2010
    Location
    miami,fl.
    Posts
    623

    duct sizing

    can anybody post a good book or website to learn how to calculate return duct sizing, and return grille sizing basically something that can brush me up and better on the airflow side.

  2. #2
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
    Posts
    2,692
    Quote Originally Posted by anthonyac1 View Post
    can anybody post a good book or website to learn how to calculate return duct sizing, and return grille sizing basically something that can brush me up and better on the airflow side.
    Return air grille = 2 cfm per sq. inch. Example: 14"x6" = 168 cfm

    One ton of A/C is 400 cfm............ 2 ton = 800 cfm. However, I size the cfm to the furnace/ air handler blower. Example: 3 ton blower requires (at least) 1,200 cfm.

    I always go more cfm rather than being right on the money or, like many contractors, not having enough return.

    If your cfm requirements are split (example) 50/50 then, with a 3 ton (1,200cfm) blower, you would need (at least) 600 cfm from one end and another 600 cfm from the other end.

    Now, for duct sizing......... take your cfm requirement, multipy by .02 and add 2.
    Example: 600 cfm x .02 = 12 + 2 = 14"x8" duct. Another example: 1,000 cfm duct requirement..........1,000 x .02 = 20 + 2 = 22"x8" duct.

    There's your book.....free and simple. There is alittle more to it of course, but the above helps our techs determine quickly short falls in systems without enough RA.

    I can look at a home (if the ductwork is easy to see) and let the customer know in 15 minutes if there is a problem with the ductwork and/or return grilles sizing.
    Last edited by George2; 12-10-2012 at 09:55 PM. Reason: spelling

  3. #3
    Join Date
    May 2007
    Location
    Dry as a bone Tucson
    Posts
    4,343
    Here is an excellent and concise pdf.
    Attached Images Attached Images
    Some Talk, Some Do
    "keeping condensing pressures low and evaporator pressures high"
    "Some customers are more interested in comfort than energy savings"
    Blog
    Web
    Facebook


  4. #4
    Join Date
    Feb 2013
    Location
    Huntsville, AL
    Posts
    80
    Acfixr..Nice pdf!Thank you.

  5. #5
    Join Date
    May 2007
    Location
    Dry as a bone Tucson
    Posts
    4,343
    Quote Originally Posted by ComfortService View Post
    Acfixr..Nice pdf!Thank you.
    You might glean some knowledge from these too then.............
    Attached Images Attached Images
    Some Talk, Some Do
    "keeping condensing pressures low and evaporator pressures high"
    "Some customers are more interested in comfort than energy savings"
    Blog
    Web
    Facebook


  6. #6
    Join Date
    Dec 2002
    Location
    SouthEast NC ICW & Piedmont Foothills
    Posts
    7,635
    check your mail, skydrive has a 35mb file
    It`s better to be silent and thought the fool; than speak and remove all doubt.

  7. #7
    Join Date
    May 2006
    Location
    St. Pete, Florida
    Posts
    10
    Thanks Acfixr for posting this info.

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