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  1. #1

    square duct size?

    My unit is up in the attic and I want to bring it down in the garage for a vertical configuration. My question is what size square duct made from duct board do I need? (3) return trunk lines 10,14,14

  2. #2
    Join Date
    Jan 2008
    Posts
    2,023
    Are you going to tell us what size the unit is, or shall we just guess?
    Air handler? Furnace? Model, serial?
    "Hey Lama, hey, how about a little something, you know, for the effort." And he says, "there won't be any money, but when you die, on your deathbed, you will receive total consciousness." So I got that goin' for me, which is nice. - Carl Spackler

  3. #3
    It will soon be a new Goodman ASPF426016E 4 ton heat pump

  4. #4
    Join Date
    Dec 2005
    Location
    Cincinnati, Oh
    Posts
    5,042
    Quote Originally Posted by electricblue View Post
    It will soon be a new Goodman ASPF426016E 4 ton heat pump
    I wouldn't put it in a garage.

    Your going to have some big code issues.

    Railing protection system, has to be so high off the floor, has to be sealed EXTREMELY tight. Your just asking for problems.

    But:
    12x32 would meet the requirement for a 4-ton heat pump.
    "Better tell the sandman to stay away, because we're gonna be workin on this one all night."

    "Dude, you need more than 2 wires to a condenser to run a 2 stage heatpump."

    "Just get it done son."

    Dad adjusted

  5. #5
    Join Date
    Jul 2011
    Location
    Waxahachie TX/stuck in Santa Clara CA
    Posts
    53
    A few questions from a non-pro...

    1) Is this a DIY project?
    2) Is duct board allowed to penetrate the wall into the garage?
    3) Which is worse, furnace and ducts in attic, or furnace in garage and ducts in attic (and garage)?
    4) Does manual J need to be redone for the entire duct system?

  6. #6
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,287
    Time for a Manual D review in order to develop an appropriate plan.
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  7. #7
    Quote Originally Posted by bluebinky View Post
    A few questions from a non-pro...

    1) Is this a DIY project?
    2) Is duct board allowed to penetrate the wall into the garage?
    3) Which is worse, furnace and ducts in attic, or furnace in garage and ducts in attic (and garage)?
    4) Does manual J need to be redone for the entire duct system?

    1 Just the plenum
    2 Idn
    3 I think ahu in attic sucks. Florida building code now requires carbon monoxide detectors if there is an attached garage. (good thing)
    4 Idn

  8. #8
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    Better get that unit tight, really tight. I was at a place my brother in law was renting. A new construction duplex with builder grade junk installed. The flex runs were totally collapsed and half hte house was like a jet engine was running, the others were underconditioned. It was an electric furnace instead of a heat pump located in central Missouri. His first electric Bill in Dec. was $600. The unit was located in the garage. There was no cover over the furnace filter slot. He might as well have left the door to the garage open. The place was such a slapped up POS. I bet the vinyl window were already leaking in the panes. But it had pretty countertops and an "open" layout. Must have that open layout (ie. fewer walls and doors, which cost more money for the builder.... but it's better that way right?).

    Are you sure you can't find a closet you're willing to give up? Could you build a utility closet that goes into the garage off the wall connecting to the garage? Building a utility closet is jsut a matter of some basic framing and and drywall. It doesn't even have to look pretty or be painted.

  9. #9
    How hard is it to do a tight install? I could build a closet...Why not just do a good job at sealing up the db?

  10. #10
    Quote Originally Posted by hvacvegas View Post
    I wouldn't put it in a garage.

    Your going to have some big code issues.

    Railing protection system, has to be so high off the floor, has to be sealed EXTREMELY tight. Your just asking for problems.

    But:
    12x32 would meet the requirement for a 4-ton heat pump.

    Any reason you wouldn't do 24x16? 24 being the depth of the unit.

  11. #11
    Join Date
    May 2011
    Location
    Fort Worth, Texas
    Posts
    49
    Using a ductulator, you can create the deminsions of the mainline pretty much any way you want. I would recommend oversizing a little just so you won't need to replace the mainline12 yrs from now, but also because you'll reduce the air friction (Temp increase and Noise) in the mainline. 4 tons = 1600 cfm's (minimum). 1800 - 2000 cfm capacity would serve you well.

  12. #12
    Join Date
    Dec 2005
    Location
    Cincinnati, Oh
    Posts
    5,042
    Quote Originally Posted by electricblue View Post
    Any reason you wouldn't do 24x16? 24 being the depth of the unit.
    Unfortunetly for yourself, you've openly admitted your doing the ductwork.

    I was already stretching myself by saying "maybe he just wants to make sure his contractor is doing it right."

    sorry, no DIY.


    What I will tell you, is that 24x16 is actually 22x14 in ductboard.

    and if your going to try and cut ductboard yourself, good luck. The guy that works with me roughed houses for 20 years, and has no idea how to use ductboard. It's complicated, and is an old skill that only those that have worked with someone who has done it, learn it correctly.
    "Better tell the sandman to stay away, because we're gonna be workin on this one all night."

    "Dude, you need more than 2 wires to a condenser to run a 2 stage heatpump."

    "Just get it done son."

    Dad adjusted

  13. #13
    I am doing the the d work. I'm an electrical contractor. I work with a/c guys all the time. I've asked one that I work with alot if he can charge my lineset and exac my old one. I'm just doing the labor. I know the forum rules no DIY... Just fishin for info.

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