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  1. #1
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    Jun 2019
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    Question on Trane air handler installation

    Hello,
    Just had a Trane 14 seer XR heat pump system installed yesterday. Question concerns the air handler portion. My contractor decided to use a modular air handler to allow it to fit in a very confined space under steps going to second floor. He did a vertical install for better future servicing where older system was a 12 year old TempStar system installed horizontally. Upon getting the old system out and bringing in the two pieces of the new system determined he did not have room for the existing cold air return ducting coming from ceiling to match up with the top of the vertical air handler. This space is approx 4 feet wide by 8 feet long with about half sitting under a portion of the steps so limited head room. He is an experienced contractor and determined that he could use the entire confined space as a large plenum. Put plastic over the exterior wall that had insulation installed and other three walls were bare sheetrock.
    Access door is really just a small maybe 30 inch by 30 inch panel that sits in a laundry room. So when system is running the air handler now has the vertical portion with the open top ( covered by a 20 x 20 furnace filter) that sucks the return air from this small enclosed room where the original cold air return ductwork was cut off and allows the cold air to flow from the cold air return service grill straight through 8 feet of the original duct work and it empties out - so to speak - into the self contained "plenum" and is drawn into the 20 x 20 opening of the new air handler. Hope this makes sense. Guess in a nutshell the small room is now working as a large plenum. Unit is cooling great, very quiet, definitely has suction from air handler as you can feel from access door when you open it. But will this shorten the life span, be inefficient, etc ? Definitely has a huge amount of return air to feed into the top of the air handler now !


    Picture one is the original cold air return duct now cut off inside the small equipment room and picture two you can see the vertical installation where was not enough room to actually connect the original duct to the top of the unit. So - the plenum idea.
    Attached Images Attached Images   

  2. #2
    Join Date
    Oct 2009
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    God's country - Shenandoah Valley, VA
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    It may work ok, but wouldn't meet code around here.

    Anything combustible, plastic, etc. is not allowed in a plenumn.
    Bob Boan


    ​You can choose to do what you want, but you cannot choose the consequences.

  3. #3
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    Oct 2009
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    It may work ok, but wouldn't meet code around here.

    Anything combustible, plastic, etc. is not allowed in a plenumn.
    Bob Boan


    ​You can choose to do what you want, but you cannot choose the consequences.

  4. #4
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    Jun 2019
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    Thread Starter
    Thank you for your reply Bob ! Guess I'll check with the county code department where I live in South Carolina.

  5. #5
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    Apr 2006
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    Tyler, Tx
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    Most new codes do not allow for using the joist space for a plenum. He needs to seal the walls of the "plenum"
    Philippians 4:13
    I can do all things in him that strengthen me.
    Apostle Paul inspired by GOD.

  6. #6
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    Aug 2002
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    Southold, NY
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    No wiring allowed either!

  7. #7
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    Jun 2019
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    Thread Starter
    Gentlemen,
    Thank you all for getting back on this. So my contractor needs to come back and properly seal up the walls with the same black plastic he used over the exterior wall insulation ? As to the wiring, not sure how he can do that. Is the exposed wiring dangerous ???

    New system is cooling okay but is this unconventional installation going to shorten the life or the efficiency of the air handler in your opinions ?

    I of course have paid him in full !

  8. #8
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    Oct 2009
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    God's country - Shenandoah Valley, VA
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    No, you can't have any plastic exposed in the plenumn. No plastic (PVC, wiring, sheeting, etc) exposed in the plenumn. No combustibles (wood, paper backed insulation, etc). It all has to be covered with Sheetrock or sheet metal.

    In other words, there cannot be anything that would catch fire, smolder or give off toxic fumes in case there were a fire.

    I don't see where this setup would have anything to do with the life expectancy of the equipment, but It may have a lot to do with the life expectancy of the occupants if there were a fire.

    The contractor chose this method, it's up to him to make it safe.
    Bob Boan


    ​You can choose to do what you want, but you cannot choose the consequences.

  9. #9
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    Jun 2019
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    Thread Starter
    Hey Bob,
    Thank you again for getting back. I unfortunately am totally out of my comfort zone on this subject and having to take the word of the contractor. He is a good contractor with 20+ years experience and a good reputation. Think the planned installation hit a problem when where the air handler was going to actually sit so everything could mate up with the supply duct end. Ended up under some steps as opposed to more height and that is where his "solution" came up. I called him and expressed my concerns about this install and he says he will address it. His idea was to put more plastic up on the exposed wires but that sounds like a no go. He had also mentioned putting some celotex (spelling ?) insulation board - stuff with foil on one side in case I got the name all wrong - so would that be a good solution. Said I will have a "plenumn chamber" when done. The bare sheetrock exposed I am assuming is okay, just as you said, anything that could catch fire is the concern. So he needs to cover the exposed romex wiring and any other insulation with something other than 4 mil black plastic ?

    Bottom line, he may just have to redo the whole thing since I just reread your reply and " no combustibles" can be exposed in the plenumn. This is a mess !

  10. #10
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    Oct 2009
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    No, no plastic!
    That means no plastic on the walls.
    Bob Boan


    ​You can choose to do what you want, but you cannot choose the consequences.

  11. #11
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    Oct 2009
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    No Celotex either, that's combustible.
    Bob Boan


    ​You can choose to do what you want, but you cannot choose the consequences.

  12. #12
    Join Date
    Jun 2019
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    Thread Starter
    Hey Bob,
    Thanks again for your replies. Any suggestions on how to make this install work ? I don't think the contractor can or will change out the air handler for one that he can hook up to the old cold air return ( cut off in picture) so all I can do is suggest how to make it safe and workable. Paid $$ for this install and did my homework checking the contractor out, didn't take low bid. But ended up with this mess. Any suggestions would be greatly appreciated.
    Thanks,
    Mike
    Last edited by beenthere; 06-06-2019 at 04:58 PM.

  13. #13
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    Jun 2019
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    Thread Starter
    Gentlemen,
    Thanks to everyone that responded on this "unusual" installation. My contractor and I spoke about it further and he is going to come out and install a different Trane air handler that will connect up to the original cold air return as it should ! I'll post here after it is done.
    Thanks again,
    Mike

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