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Thread: Who is right?

  1. #1
    Join Date
    Apr 2005
    Location
    Virginia
    Posts
    176
    I had a debate with another guy who has been in the business for about 40 years (myself only 10 years), about static pressure. I was under the impression that the longer the duct run including all boots,takeoff fittings,last run from duct to boot, etc., etc. that the duct would have to be smaller to build up static pressure. But he says that duct should be bigger to build up volume pressure.Who is correct?

  2. #2
    Join Date
    Nov 2001
    Posts
    1,874
    Maybe it's a miss communication type thing.

    Does he run his trunk line bigger as it gets further from the plenum ? If so he's wrong.

    If you run a trunk 30 ft, and take off 10 runs, theres not going to be any staic pressure to force the air to the last runs , if you make the duct larger as you go.
    If you try to fail, and succeed.
    Which have you done ?



  3. #3
    Join Date
    Mar 2004
    Location
    st. mary's co. md
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    86
    By rule of thumb, the ducting should become smaller the longer the run.

  4. #4
    Join Date
    Dec 2002
    Location
    Houston,Tx.
    Posts
    16,113
    Originally posted by newton
    By rule of thumb, the ducting should become smaller the longer the run.
    Unless of course the blower is powered by a jet engine then you can make the duct larger the longer it is.
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  5. #5
    Join Date
    Jul 2004
    Location
    midwest
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    2,868
    If I am reading your question right the duct needs to be bigger the farther you go and the more turns you add to move the same amount of air.




  6. #6
    Join Date
    Mar 2004
    Location
    st. mary's co. md
    Posts
    86
    Originally posted by mrbillpro
    Originally posted by newton
    By rule of thumb, the ducting should become smaller the longer the run.
    Unless of course the blower is powered by a jet engine then you can make the duct larger the longer it is.
    If this guy's been in the buisness for 40 years, I'd be scared to let him touch my house!

  7. #7
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,594
    Are you sure he doesn't mean All the duct has to be bigger to mainimize static pressure loss, (eg, a .04 fr, instead of .1)?
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