what to do when almost nothing comes out of supply vent.

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  #1  
Old 11-02-12, 07:08 PM
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what to do when almost nothing comes out of supply vent.

I had to remove a ductboard branch and replace it with six inch flex. The take off is from the trunk about two feet from transition plenum from the air handler. Now hardly any air blows out of the flex duct. I have to double check for obstructions but it's a short run and I'm almost certain there are no obstructions. I checked to make sure it wasn't being squeezed or crushed. It is not. It's like the air is blowing right past the collar. Any suggestions?

Thank you
 
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Old 11-06-12, 07:23 AM
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Add some kind of cowl?

Reduce the flow at the registers on the main trunk to increase the pressure in the main duct so that more gets directed to the flex?
 
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Old 11-06-12, 06:01 PM
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yep, add an air scoop. It doesn't have to be large.
 
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Old 11-16-12, 08:10 AM
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Thank you both for the suggestions. I thought about that scoop possibility as well, though I'm not sure what to use for the scoop or how to attach it to the collar inside the trunk. Maybe a 90 elbow or cutting a pipe in half and attaching somehow? Any suggestions?
I've tried using the dampers at the other grills, but not much seems to happen.
 
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Old 11-18-12, 06:44 AM
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Two feet is to close. The air has not had time to fill the duct yet because its still rolling from coming of the blower. I'd add a scoop as suggested or move the collar. A blank peace of sheet metal will work fine
 
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Old 11-18-12, 10:38 AM
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Yeah, thought of that possibility also. Funny thing is, I added another supply collar(4 inch) in front of this one directly on the transition plenum and this one does have air blowing, though not as much as I'd hoped. After sealing all the ducts I still have some of the same issues where larger supply boots directly off of the trunk and closer to the supply plenum have less air blowing than boots that are at the end of the trunk and smaller branches also further from the supply plenum. Doesn't seem to make sense. Thanks for the reply.
 
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Old 11-18-12, 07:45 PM
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Residential systems work by pressurizing the main trunk. So the farthest lines from the AHU will have more air
 
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