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  1. #14
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    Jan 2004
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    Lancaster PA
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    Bottom return only is ok for 5 ton system.
    A single side return only would not be ok.
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  2. #15
    Join Date
    Jun 2008
    Location
    Dallas, TX
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    11
    Thanks for the inputs.

    I noticed on udarrell's website that it says a 5 ton system needs two filter racks 20x25 to give 1000 sq in of surface area. I have just one filter rack with the 5" pleated media filter. Is this OK or could that be an issue?

    From what I calculate with the (4) 16x16 returns, and 12" ducts, I am getting enough return flow. However, when I add the CFM ratings of all of the output ducting using (8) 8" flex ducts at approx 180 CFM each (from the udarrell site), I get only 1440 CFM. That could be a reason for the high static pressure I assume?

  3. #16
    Join Date
    Jan 2004
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    Lancaster PA
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    There are some media filters rated at 2000 CFM. They work ok. 2 of them is better.
    Your media filter may havea pd of .25 or much greater with a media. Depending on MERV rating nad manufacturer.
    What size is yours 20 x 25? Or smaller.

    Udarrels site is ok.
    Its the length of the run also that determines how much air you have through those 8" supplies.
    They are most likey part of the cause of your high static.
    The length of your 12" return ducts also determines how much air is returned to your unit, and may be a cause of your high static.
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  4. #17
    Join Date
    Apr 2008
    Location
    Alberta Canada
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    2,246

    Correct Installation

    [QUOTE=zz4x4;1894356]

    What is your last 2 numbers on model # 58CVA110 - _ _.
    Anything over 1600 cfms should either come in the bottom of furnace or 2 sides of furnace for friction and air volume. At 1750 CFMs (350 per ton) you need at least 160sq" of supply air duct and approximately 225 sq" return air. At 2000 you should have 170sq" of supply and approixmately and 270 sq" on return. Send picture and then I can see everything.
    Do it right the first time.

  5. #18
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
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    18,836
    [QUOTE=21degrees;1894562]
    Quote Originally Posted by zz4x4 View Post

    What is your last 2 numbers on model # 58CVA110 - _ _.
    Anything over 1600 cfms should either come in the bottom of furnace or 2 sides of furnace for friction and air volume. At 1750 CFMs (350 per ton) you need at least 160sq" of supply air duct and approximately 225 sq" return air. At 2000 you should have 170sq" of supply and approixmately and 270 sq" on return. Send picture and then I can see everything.
    160 sq in of supply would be a FR of of almost .2 in. of wc,way too hiogh ,return wpuld be too highn of a FR as well.

    Really without a Man. D for th entire duct system,you can't say for sure what size ducts.That said using a FR of .06 might get you in the balpark.Fr of .06,would be a 14X20 supply ,at 1750cfms,and 280 sq in..

  6. #19
    Join Date
    Apr 2008
    Location
    Alberta Canada
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    2,246

    Sorry

    [QUOTE=dash;1894600]
    Quote Originally Posted by 21degrees View Post

    160 sq in of supply would be a FR of of almost .2 in. of wc,way too hiogh ,return wpuld be too highn of a FR as well.

    Really without a Man. D for th entire duct system,you can't say for sure what size ducts.That said using a FR of .06 might get you in the balpark.Fr of .06,would be a 14X20 supply ,at 1750cfms,and 280 sq in..
    Sorry I was going off top of my head. Man I fined that hard to beleive. The biggest duct I have ever ran was 12 X 20 on 2 stage 5 ton. I have never seen duct work that big. I thought I was going nuts when I ran this. Even builder said he has been building house for thirty years and bigger. Never seen duct work like this Even though I did it right he probably thinks I'm 1 can short of six pack. I do not do 5 tons to often, but always use ductulator on quotes.
    Do it right the first time.

  7. #20
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    Jan 2004
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    Lancaster PA
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    12 x 20 is small for a 5 ton, unless your trunk is super short, or you had a second duct coming off the plenum.
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  8. #21
    Join Date
    Jun 2008
    Location
    Dallas, TX
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    11
    What size is yours 20 x 25? Or smaller.
    The filter is a Merv 11, 20 x 25 x 5

    What is your last 2 numbers on model # 58CVA110 - _ _.
    Not sure. On the Model / SN screen it shows 58CVA110---1. Is there somewhere else it might be located?


    I have some photos ... Could the spider of supplies coming from the sides of the supply plenum cause the pressure? I noticed even in low speed operation I am getting 1400 CFM and 1.01 SP according to the controller.
    Attached Images Attached Images     

  9. #22
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    Jan 2004
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    Lancaster PA
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    You have atleast 2 supplies that are restricted near the supply plenum.
    In the first pic, the return flex on teh right is too hard of a 90 to get good air flow through it.

    With both of teh return flexs being close together, and right at the filter, it causes turbulance. very restrictive.
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  10. #23
    Join Date
    Aug 2006
    Location
    Marco Island, Fl
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    729
    This is a quick test to help how bad the supply is restricted. (the supply is among the worst supply take-offs I have ever saw)

    Take the cover off the filter and remove the filter. Leave the filter out and the cover off. Let it draw air from the attic. Get fan to at least 1750 cfm (preferably 2000 cfm) and read the static pressure. This will pretty much tell you the discharge static.

    Your original high speed static of 1.2+ minus the newly read static will be your return static.

    From the duct sizes listed and the photos, the quality of the install is the big culprit here.

    You have definite supply and return duct issues, but even larger ducts will not compensate for poor work like that.

    There appears that there is room in the attic to easily and properly correct the problems on both the return and supply side.

    Poor installs like this are what give flex duct a bad rep.

  11. #24
    Join Date
    Jun 2008
    Location
    Dallas, TX
    Posts
    11
    Davo,
    I did as requested but was unable to read static pressure with the filter door open. Just reads UNKNOWN. If I leave the filter out , but still close the door, the SP reads 0.9 . Looks to be .3 difference across the filter. Does that seem reasonable?

  12. #25
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    Jan 2004
    Location
    Lancaster PA
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    Thats not an unusual drop across a media filter.
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  13. #26
    Join Date
    Jun 2001
    Location
    Louisville, KY
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    12,172
    Quote Originally Posted by zz4x4 View Post
    I have some photos ... Could the spider of supplies coming from the sides of the supply plenum cause the pressure? I noticed even in low speed operation I am getting 1400 CFM and 1.01 SP according to the controller.
    That is horrible.

    I think I'll use those pictures for future training classes on how to NOT install flex duct.
    Perhaps you should have read the instructions before calling.

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