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  1. #14
    Join Date
    Dec 2002
    Location
    Houston,Tx.
    Posts
    16,111
    Just FYI in case no one has told you yet the TD "temperature differential" is not measured from return air grille to supply grilles, it's measured across the coil from the return air can on the furnace to the plenum were all the ducts take off, if you getting a 16 to 20 degree differential there you are good to go, you will automatically have "some" heat gain in all ducts unless it's maybe a two foot run.
    __________________________________________________ _______________________
    “Experience is a hard teacher because she gives the test first, the lesson afterwards". - Vernon Law

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  2. #15
    Join Date
    Dec 2007
    Location
    Houston, TX
    Posts
    29
    Thanks mrbill, I do understand where the temperature differential should be measured.
    I am going by the fact that when the installer measured at the coil the temps were almost the same at the return ( unit sits directly above the wall return) and the supply register in the closest room ( about 4 ft from plenum).

    Thanks again, Your input is appreciated. I had talked to you on the phone when I had this unit installed ( You worked too far from Pasadena to do the job ).

  3. #16
    Join Date
    Dec 2007
    Location
    Houston, TX
    Posts
    29

    I don't think my hotter rooms are getting enough air

    Thanks to all especially accutrol & mr. bill

    I have spent all afternoon checking temps and looking in the attic.
    when the thermostat shuts off I have 3 rooms that are hotter than the set point & they are all the new flex which is all R8. The 2 hotter rooms actually come off the same line from the top of the plenum which is about 25' of 9" flex then a triangular box with about 5' of 7" and about 25' of 7" going to the rooms. I also have another room with about 8' of 7" that is kind of crumpled up looking. All 3 of these rooms are getting less air flow from the registers than the other rooms. The other rooms have a lot of airflow. Installer told me the blower was set up for 400cfm per ton x 4 ton. I will have my installer come out with his hood and check air flow before installin a txv valve.
    About what should my cfm ratings be on return and supply registers ??

    Thanks again to all.

  4. #17
    Join Date
    Jan 2008
    Location
    lexington, kentucky
    Posts
    50
    It is my opinion, just my opinion, that the 9" flex into the triangular box is not a standard practice. At least not here in kentucky. Each room should have it's own flex run from the plenum. I have never used this method of supplying air to romms, nor will I ever use it. Maybe if they had put 1 8" run to each room, that might help the problem.

    I still say there is too much flex there. There should have been some duct run towards the area where the 2 rooms are located.

  5. #18
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,586
    Running a larger flex to a pie is common in some areas. Nothing wrong with it if its sized right.
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  6. #19
    Join Date
    Jan 2008
    Location
    lexington, kentucky
    Posts
    50
    Might be, but to me it is just a cheap way for an installer to try to get air to a far away area when properly sized ductwork would achieve such better results.

  7. #20
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,586
    If the flex to the pie, and the flex to the registers are sized properly, then it is a properly sized duct system.

    Key phrase is properly sized.

    You can run a metal duct that is undersized and it won't work.
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  8. #21
    Join Date
    Jul 2005
    Posts
    435
    Just a thought, could an additonal return at his far side of the house where he is having his cooling issues fix this problem?

  9. #22
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,586
    If lack of return is the problem, yes.
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  10. #23
    Join Date
    Dec 2002
    Location
    Houston,Tx.
    Posts
    16,111
    I don't like or ever use triangle boxes "period" we use wyes "sometimes" when we are going to a bedroom and a short run to a small bath only, but as another poster said it's really better to run dedicated runs to all rooms with dampers on each collar of each run, that way trust me you won't be having these issues, or if you do you have the ability to close or open dampers to every room to get what air you need were you want it.
    __________________________________________________ _______________________
    “Experience is a hard teacher because she gives the test first, the lesson afterwards". - Vernon Law

    "Never let success go to your head, and never let failure go to your heart". - Unknown

  11. #24
    Join Date
    Dec 2007
    Location
    Houston, TX
    Posts
    29
    accutrol,
    these 2 rooms were a problem for my old system to cool. the old hardpipe supplied these 2 rooms and the kitchen. these 2 rooms were taken off the hard pipe and the flex ran to them. the old hardpipe now supplies the kitchen only and keeps it cool.

    kevinmac,
    the farthest room has a new 14" flex return with a 14" x 25" grill mounted in the ceiling.

    thanks

  12. #25
    Join Date
    Dec 2002
    Location
    Houston,Tx.
    Posts
    16,111
    Quote Originally Posted by 2elaines View Post
    the farthest room has a new 14" flex return with a 14" x 25" grill mounted in the ceiling.

    thanks
    What you need to do is measure all your duct take offs at the plenum and post it along with the cfm's of your system and we can tell you if it's even in the park. You can have to large of duct runs and IMO it does give you volume, but it kills your pressure and it sounds like you need more pressure to these furtherest rooms. If all your duct is oversized to all rooms good luck getting air to the needed rooms.
    __________________________________________________ _______________________
    “Experience is a hard teacher because she gives the test first, the lesson afterwards". - Vernon Law

    "Never let success go to your head, and never let failure go to your heart". - Unknown

  13. #26
    Join Date
    Dec 2007
    Location
    Houston, TX
    Posts
    29
    ok, so you need diameter of each line and length ??

    Does the position on the plenum matter as most all are on one side and the top.

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