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  1. #27
    Join Date
    Mar 2005
    Location
    Suppy NC
    Posts
    4,516
    since there is no pratical way to replace the intire duct it would seem to make sence to move it to the top of the pleun. make it a 12 in take off anr run the flex as clos to where it goes under the floor. it will start at about 550 to 600 cfm and restrict down to hopefuly 400 at the arrow head. this should increase the stadic pressure of the flex. then install another outlet in your bedroom if you can. this will give you more air flo the trying to get though two six in runs. you will now have three six in run and about 375 cfm give or take a little. the question here that is important is how many cfms will the system deliver
    what size is the airhandler. model # of unit will help because if it is not big enough what ever you do will make no differance at all

  2. #28
    Join Date
    Jul 2004
    Posts
    322
    Originally posted by tinknocker service tech
    since there is no pratical way to replace the intire duct it would seem to make sence to move it to the top of the pleun. make it a 12 in take off anr run the flex as clos to where it goes under the floor. it will start at about 550 to 600 cfm and restrict down to hopefuly 400 at the arrow head. this should increase the stadic pressure of the flex. then install another outlet in your bedroom if you can. this will give you more air flo the trying to get though two six in runs. you will now have three six in run and about 375 cfm give or take a little. the question here that is important is how many cfms will the system deliver
    what size is the airhandler. model # of unit will help because if it is not big enough what ever you do will make no differance at all
    I've got a Carrier 4 ton variable speed air handler that can get me slightly over 1600 cfm according to the manual. Set at 350 cfm/ton it gives excellent cooling except to the master bedroom.

  3. #29
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    5,031
    Originally posted by dash
    Originally posted by udarrell
    Use the 10" takoff and Run the 10" duct out as far as you can then go the reducer to 8 inches. That "might" (too many unknowns) get it closer to 250-cfm but will increase the velocity through the boot and diffuser.

    http://www.udarrell.com/proper_cfm_b...g_systems.html


    The friction rate quoted in your site is not applicable to all duct systems,many need to be designed at .06 or .08,as opposed to .1 or .09.A manual D design will give you the correct FR for every job.
    You are right, I should have emphasized that they use the manual D, and will make a note of that on that page. Actually, I should have made a note that the chart sizes actually vary from .06 to .1, not very professional, huh.

    It was meant to be a rough guide for equipment owner's to do a ball park check on the sizing of their duct systems.

    The pros ought to know to use the manual D for ductwork.

    When larger residential A/C equipment is installed many times the duct system ends up being undersized. Thank you "dash" for jacking me up, I should have explained the variation parameters involved in the rough chart.

  4. #30
    Join Date
    Aug 2002
    Location
    manitowoc wisconsin
    Posts
    4,943
    There is a little more than just size to consider.Is it an adjustable takeoff or straight?Is the take off leaving the plenum in the same direction as air flow?Is there a scoop take off directly below the take off?Is it placed to close to a blank end of an a-coil?You can put in a twenty inch take off & see little improvement if it is not installed properly.
    Take your time & do it right!

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