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  1. #1
    Join Date
    Mar 2009
    Location
    Toronto, Ontario
    Posts
    9

    Question Advice - AC Coil extending past plenum

    Hi,

    This week I had my new furnace and AC installed.

    I have a concern that the AC coil extends 5.5" from the plenum.

    I know that was an issue with my previous system and am having a hard time seeing how I am getting full benefit of the AC with a portion of it extended from the air flow.

    I am by no means a HVAC expert, so if this is normal and there is no impact to the system cooling efficiency then I am fine. However, if there is an impact do I need to look at a bigger plenum?

    My preference is to have the system running at it's peak and not hampered in any way.

    I'm hoping that the pros here will let me know what their recommendations are and why.

    Thanks,

    Dolfan

  2. #2
    Join Date
    Feb 2003
    Location
    garland, texas
    Posts
    677
    A picture would be most helpful.

  3. #3
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,369
    Quote Originally Posted by nvr2old View Post
    A picture would be most helpful.
    Yes. We don't know if the OP is talking about a horizontal unit in the attic, or an upflow unit in a hall closet, or one or the other in a basement/crawl space.

    Generally speaking, it is best to not intentionally blank off a section of cooling coil, as some installations do. This is what transitions are for should the coil be larger than the air handler or furnace dimensions.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  4. #4
    Join Date
    Nov 2008
    Location
    Chapel Hill, NC
    Posts
    1,070
    Do you mean the AC coil box is wider than the plenum? If so, that's OK, you just don't want a coil box that is narrower than the plenum or furnace as that would cut air flow down significantly.

  5. #5
    Join Date
    Sep 2002
    Location
    Northeast Ohio
    Posts
    4,854
    Need pics
    A good HVAC tech knows how, an educated HVAC tech knows why!

    DEM


  6. #6
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    5,025
    This has become a problem with the higher SEER coils & lack of room, etc. to make proper retro adjustments.

    The main thing is that the entry through the coil be open to a straight stream of airflow. Also, the drain pan, if not insulated, may sweat if out of the air stream.

    It is very important to have equal distribution of air through the coil circuits.

    Unequal distribution will result in lack of liquid evaporation which affects suction superheat.

    Due to a colder line, a TXV would tend to reduce the flow of refrigerant to the coil.

    Charging by superheat will also be OFF. Both superheat & subcooling should always be checked on all systems & compared to what they should be.

    If at all possible have the retro work done to correct any airflow problems.
    - Darrell

  7. #7
    Join Date
    Mar 2009
    Location
    Toronto, Ontario
    Posts
    9
    Will take pics tonight and post them.

    I'll try to explain it further...

    Basement install (Toronto, Canada).

    Code:
             |       |  Plenum
             |       |___
             |            |
             | Coil       |
             |        ___|
             |       |
             |       |         
             |            |
             |            |
             | Furnace|
    Pics will be uploaded tonight when I get home

  8. #8
    Join Date
    Nov 2008
    Location
    Chapel Hill, NC
    Posts
    1,070
    Hmmmm.......... It looks like the coil is offset from both the furnace and the plenum airflow and not uniformly extending out on all 4 sides. This could be a problem. Post pics!

  9. #9
    Join Date
    Mar 2009
    Location
    Toronto, Ontario
    Posts
    9

    Pictures attached

    Here are the pictures....

    Please provide your feedback.

    Thanks,

    Dolfan
    Attached Images Attached Images    

  10. #10
    Join Date
    Jun 2006
    Location
    Richmond, VA
    Posts
    2,980
    Those should go on the wall of shame, that is not right, won't work right, words cannot describe the my shock when i saw these pics.

  11. #11
    Join Date
    Jan 2008
    Posts
    2,089
    Wow. Wall of shame is right. Someone did some poor work for you there.
    "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

  12. #12
    Join Date
    Aug 2008
    Location
    Burlington , Mass
    Posts
    470
    Just when you thought you've seen everything.


    It does look as though the coil was already in that position before the new furnace was installed. and they just transitioned to it as the new furnace is shorter. Even if it was that way, the installer should have mentioned that its improper.


    You should get a new cased coil installed on the furnace ( matched to the furnace opening ). The manufacturer of the furnace will have a matching enclosed coil set up.
    I'll be there when I get there and not a minute later

  13. #13
    Join Date
    Apr 2008
    Location
    Galion, Ohio
    Posts
    83
    wow...if I did that i would be fired.....lol

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