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  1. #14
    Join Date
    Jul 2005
    Posts
    12
    I'm sure all the duct work needs replaced but was told it would be fine for a few years.

    Sounds like the return duct needs a re-do.

    I'm no AC guy, just trying to learn, hopefully not from my mistakes.

  2. #15
    Join Date
    Jul 2005
    Posts
    12
    bkliewer - I was coached this direction by a few AC guys.

  3. #16
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,914
    I see 5 ton systems with one 16" flex duct for a return.
    In reality, one 16" return duct to a 20x25 filter grill is less than 1/2 of the return ductwork a 5 ton system needs to operate properly.
    If more government is the answer, then it's a really stupid question.

  4. #17
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Originally posted by bubstang
    It appears the airbox gets reduced down to an 18" square inlet to the furnace and then 16" round duct to the return air. Not sure I'm calling these things right, but hopefully you know what I mean.

    You guys want pics?
    Sure post some pics!!


    Since the return is that small,I'd take a close lok at the suppy ducts as well.

    If it only runs a short distance with one 90(turn),it not as bad as 40' and several 90's.

    Is the furnace being replaced as well?If so ,and it has a variable speed motor,expect more air noise,as they can move more air then a standard PSC motor.

  5. #18
    Join Date
    Jul 2005
    Posts
    12
    the air handler/furnace is a T8MPN100F20A1. The manual says (2)16"x25" for 5 ton.

    From there can I assume/guestimate that a 20" return would suffice?

    Is there an online refence? or is Manual D the guidebook.

    Don't get me wrong, I like your input because it seems practical and experience based.

    Thanks,
    Robert

  6. #19
    Join Date
    Jul 2005
    Posts
    12
    The 16" duct is maybe 12' long. Pretty much straight from the vent, then has one 60-90 degree bend into the box.

    There is no variable speed, seems pretty quite as of now.

    Going off to take some pics. Be back in a few.

  7. #20
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Without a VA motor,it's not able to deliver the required air flow,so noise won't be a problem.

    Without required air flow:
    1.Less btu output,costs you more to oprerate.

    2.If it's low enough ,early compressor failure.

    3.Rooms farthest from the furnace might not get enough air and can
    be warmer/cooler then others depending on the season.

  8. #21
    Join Date
    Jul 2005
    Posts
    12
    so is the best thing to have the 16" change out to a 20" or just add another 16" with another 20x25 return?

  9. #22
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Adding another return is usually easier in our area,depends on the constrution,often difficult to find a location for the correct size grille for a large system,with two it's easier.

  10. #23
    Join Date
    Jul 2005
    Posts
    12
    thanks a bunch guys!

    You've been a big help.

    Robert

  11. #24
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Ask them to measure the Total External Static Pressure(TESP),of the supply(including the coil),and the return ducts(including the filter).

    This is one way to insure proper air flow.

  12. #25
    Join Date
    Jul 2005
    Posts
    12
    what should the TESP be? Is there an ideal range?

    Thx

  13. #26
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    It depends on the furnace ,post the model number and someone may have that info.


    Usually up to.6 or .7 in the specs.,though many here will say .5 TESP.

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