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  1. #1

    Having a 8.5 ton unit installed and have some ?'s

    New to the forum so "Hello to every one"

    I am getting some quotes to have an 8.5ton a/c unit installed and wanted to better understand the need for large ducting.

    In one of our other buildings which is much larger there is 12" ducting running from 3 different a/c units. which are cooling a larger area.

    In one of my quotes the ducting is almost 3 times bigger than the 12"

    This unit is bigger than the other ones but is cooling a smaller area why do I need such large ducting? Also do I need as big ducting for the return? lastly does it matter if the ducting is installed near the roof or could it be down low? (being the unit will be installed at ground level and the ducting will have to go through the wall.)

  2. #2
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    7,049
    8.5 tons requires large duct, that's ~3400cfm of air flow. Probably somewhere in the 32-36" diameter round duct.

  3. #3
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,184
    12" metal pipe is good for about 1/2 ton worth of airflow. So if you were running 12" pipe for a 8.5 ton, you'd need about 17 runs!

  4. #4
    Join Date
    Aug 2002
    Location
    Southold.calm
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    5,701
    Quote Originally Posted by BaldLoonie View Post
    you'd need about 17 runs!
    Minimum

  5. #5
    Quote Originally Posted by jtrammel View Post
    8.5 tons requires large duct, that's ~3400cfm of air flow. Probably somewhere in the 32-36" diameter round duct.
    So the return Would have to be the same size as well?

  6. #6
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    7,049
    Quote Originally Posted by eroc View Post
    So the return Would have to be the same size as well?
    Or slightly larger.

  7. #7
    Join Date
    Dec 2000
    Location
    Flat Rock, NC
    Posts
    463
    With duct size answers like this who do you get approved to reply to AOP questions?

  8. #8
    Join Date
    Aug 2004
    Location
    S.E. Pa
    Posts
    6,192
    Quote Originally Posted by codgy View Post
    With duct size answers like this who do you get approved to reply to AOP questions?
    This is the Ask Our Pro's or AOP forum. In order to post responses here, you must have verified qualifications and have been approved by the AOP Committee. Please see my signature line for links to register and review the AOP Forum Rules. Thank you.

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