Page 1 of 2 12 LastLast
Results 1 to 13 of 19

Thread: Duct Problems

  1. #1
    Join Date
    Apr 2006
    Location
    Columbus, Ohio
    Posts
    802

    Duct Problems

    Today i had a water source heat pump feeding a classroom and 3 offices. It has a main trunk line with 8" taps coming off of it. There are a total of 7 taps on this unit. 4 for the classroom and 1 for each office. Well the problem i am having is the one diffuser nearest to the unit isn't putting out hardly any air. I pulled the duct off and inspected inside the duct. At this point in the duct, it is like there is a dead spot. The air is just turbulating around the opening. This duct tap comes off right after the flex connector. It is the first fed. The diffusers that come off further down the main get plenty of air. Why is this? What can i do to the ducting to fix this problem? The office with the problem has the stat. So it is causing no heat or cool to go into the room. So it either burns everyone out or freezes everyone out depending.

    Thanks for the help!
    J. King

  2. #2
    Join Date
    Sep 2007
    Location
    Boise, ID
    Posts
    4,287
    Too high of velocity, the air just blows on by. Add a scoop.

    Oops, hope that aint DIY. If so a mod can remove and spank me.
    If a nation expects to be ignorant and free, in a state of civilization, it expects what will never be. (Thomas Jefferson 1816)

  3. #3
    Join Date
    Oct 2007
    Location
    Milwaukee,WI
    Posts
    1,071
    How many people have messed with the downtream dampers to get more/less heat or cooling in their office?

    A simple professional re-balance may help things. Either that or it may not have been properly balanced in the first place.
    ___________________________

    Chicago is an indian word for stinky!!!!!!
    -supertek65

  4. #4
    Join Date
    Oct 2010
    Location
    AZ
    Posts
    647
    How far away is this duct from any changes in direction?
    Is there a long section of straight duct before the tap or is it right after a change in direction?
    Do you have shoe taps?

  5. #5
    Join Date
    Apr 2006
    Location
    Columbus, Ohio
    Posts
    802
    Too high of velocity, the air just blows on by. Add a scoop.

    Oops, hope that aint DIY. If so a mod can remove and spank me.


    Yea i was thinking that, but i just didn't know how much that would help. I haven't used them that much. I heard something from a sheet metal guy stating that the air is more even at the end of the trunk.

    How many people have messed with the downtream dampers to get more/less heat or cooling in their office?

    A simple professional re-balance may help things. Either that or it may not have been properly balanced in the first place.


    Actually every damper is open all the way down the trunk line.

    How far away is this duct from any changes in direction?
    Is there a long section of straight duct before the tap or is it right after a change in direction?
    Do you have shoe taps?


    The main duct just comes straight off of the heat pump, goes into a flex connector, and is just a straight run all the way to the end cap. The duct doesn't change directions or switch sizes. The tap with the problem is right up next to the discharge of the unit. There is no long straight run before the taps.

    Shoe taps? Are they taps with scoops?
    J. King

  6. #6
    Join Date
    Sep 2007
    Location
    Boise, ID
    Posts
    4,287
    Might want to relocate the takeoff further down the duct where there is less turbulence and and the velocity has slowed, probably the easiest solution.
    If a nation expects to be ignorant and free, in a state of civilization, it expects what will never be. (Thomas Jefferson 1816)

  7. #7
    Join Date
    Oct 2011
    Location
    Arkansas
    Posts
    835
    Quote Originally Posted by apprentice3 View Post
    Today i had a water source heat pump feeding a classroom and 3 offices. It has a main trunk line with 8" taps coming off of it. There are a total of 7 taps on this unit. 4 for the classroom and 1 for each office. Well the problem i am having is the one diffuser nearest to the unit isn't putting out hardly any air. I pulled the duct off and inspected inside the duct. At this point in the duct, it is like there is a dead spot. The air is just turbulating around the opening. This duct tap comes off right after the flex connector. It is the first fed. The diffusers that come off further down the main get plenty of air. Why is this? What can i do to the ducting to fix this problem? The office with the problem has the stat. So it is causing no heat or cool to go into the room. So it either burns everyone out or freezes everyone out depending.

    Thanks for the help!
    How long is the plenum?

    Usually with that many take offs and a long plenum, it's best to reduce it. A scoop would help, but a new properly sized plenum would be the best solution.

  8. #8
    Join Date
    Sep 2011
    Location
    Vancouver, WA
    Posts
    259
    Quote Originally Posted by apprentice3 View Post
    Too high of velocity, the air just blows on by. Add a scoop.

    Oops, hope that aint DIY. If so a mod can remove and spank me.


    Yea i was thinking that, but i just didn't know how much that would help. I haven't used them that much. I heard something from a sheet metal guy stating that the air is more even at the end of the trunk.

    How many people have messed with the downtream dampers to get more/less heat or cooling in their office?

    A simple professional re-balance may help things. Either that or it may not have been properly balanced in the first place.


    Actually every damper is open all the way down the trunk line.

    How far away is this duct from any changes in direction?
    Is there a long section of straight duct before the tap or is it right after a change in direction?
    Do you have shoe taps?


    The main duct just comes straight off of the heat pump, goes into a flex connector, and is just a straight run all the way to the end cap. The duct doesn't change directions or switch sizes. The tap with the problem is right up next to the discharge of the unit. There is no long straight run before the taps.

    Shoe taps? Are they taps with scoops?
    The rule of thumb I use is the first tap has to 3 times the diameter of the duct away from the discharge of the unit. So if the duct is 8" dia, then your first tap is set at 24" away from the unit. This also applies to change of directions.

  9. #9
    Join Date
    Jan 2001
    Location
    Pamnyra VA.
    Posts
    710
    Is there a transition in duct size anywhere along the main trunk?There should be after a few taps are taken off.This will add pressure to your outllet.

  10. #10
    Join Date
    Jun 2010
    Location
    Philadelphia PA
    Posts
    2,190

    Gibby, I like this suggestion

    Quote Originally Posted by Gib's Son View Post
    Might want to relocate the takeoff further down the duct where there is less turbulence and and the velocity has slowed, probably the easiest solution.
    I'd be a little uncomfortable with a "scope" that might really disrupt the high velocity air stream coming off the unit as per your first thought
    You have got to learn from other people's mistakes! Because God knows you don't live long enough to make them all yourself !!!!!!!!

  11. #11
    Join Date
    Aug 2007
    Location
    Northern VA 38 degrees N by 76 degrees W
    Posts
    5,060
    +1

  12. #12
    Join Date
    Sep 2007
    Location
    Boise, ID
    Posts
    4,287
    Quote Originally Posted by genduct View Post
    I'd be a little uncomfortable with a "scope" that might really disrupt the high velocity air stream coming off the unit as per your first thought
    I kinda missed the turbulence word first time around. That being said, I have seen it many times with high velocities that the air just rushes on by the first branch.
    If a nation expects to be ignorant and free, in a state of civilization, it expects what will never be. (Thomas Jefferson 1816)

  13. #13
    Join Date
    Jul 2011
    Location
    Columbus, Ohio
    Posts
    136

    No static man

    Sounds like you have no static pressure. Too many openings or too many air exits to allow for static pressure to build up and push the air out of the closest registors. Close down some of the dampers until you get static pressure in the trunk. I Should think you would need a 1/2 inch or so of pressure at 2/3 down the trunk run, on a unit that size.

Page 1 of 2 12 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event