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Discussion Starter #1
I have a duct system the comes out directly straight and the that feeds about half the house. About 7 feet out away from the plenum, an arm breaks off in a straight 90 degree (all soft ducting after the initial connection to the plenum).
...anyway, have difficulty getting air to the 90 degree arm and have to believe its because of the poor design. No matter how much I try to restrict the other side of the house with dampers, it does nothing (just louder and comes out harder).

...if that is the issue (the straight 90 degree arm that feeds 1/2 the house), is there a way, outside of installing a zone, to simply deflect or reduce the airflow on the "main" straight line...or divert more air into the 90 degree turn?

Any help or guidance would be much appreciated!

Mike
 

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Is all that flex?
You can’t ever tap into the end of a duct. You’ll make a path of least resistance and create a problem like your currently experiencing.
 

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Is any of your duct accessible? You are going to have to change a few things since installing dampers will most likely make it perform poorly overall.
 

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Air is reluctant to change directions and that air we would like to cool/heat that problem area is having to bend 90° twice then a lesser angle at the far end to those registers. If we add this direction change we're looking at 180° direction reverse at minimum. It looks to me there needs to be a change at the plenum..
 

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Discussion Starter #5 (Edited)
Air is reluctant to change directions and that air we would like to cool/heat that problem area is having to bend 90° twice then a lesser angle at the far end to those registers. If we add this direction change we're looking at 180° direction reverse at minimum. It looks to me there needs to be a change at the plenum..
I agree...i know the system is not perfect but its oversized even for my area...phoenix. its a 5 ton 15 seer Trane, 3 years old, cooling a 2000 square foot area that is well insulated with foam ceiling and batt walls (with some brick wall unfortunately but they are east facing)...only 9 ft ceilings.

I want to "band aid" the situation and was hoping to add something just beyond the plenum (or add another square plenum and evenly split from there) to get better air to the "bad" side. I was hoping I could add some sort of solution that would help with the initial 90 degree arm. the rest of the drawing is less than accurate as I was just trying to show the rough registers being serviced.

ideas?


thank you so much!!

edit: the area is cooling for sure but only to 76 during day and 71 at night. I like it freezing and think the system should be able to do that. we cool much larger areas with less tonnage on our homes and hoping we can do the same with older system (we build new).
 

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Discussion Starter #6
even a small improvement would probably do the trick as we are not that far off from the existing system doing the job....and this is by far the worst time of the year in phoenix. we have one more month of round the clock 100 degrees (or close) and then we start to cool down in evenings which really helps the system work better.
 

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I'll try again....are your ducts accessible?
Where is your air handler located?
 

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Fix the end taps.
I’m not sure how you want to bandaid a duct system that’s already a mess. Nothing to really bandaid there.
 

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Good points made above.

One thing to add - if your elbows feeding the problem area are flex switching those to insulated metal could help.
 

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Discussion Starter #11
Is any of your duct accessible? You are going to have to change a few things since installing dampers will most likely make it perform poorly overall.
yes and no....I have been a GC for 20 plus years and knowledgeable in most trades, with the exception of HVAC...we build almost exclusively new and rarely have to deal with previous "work". That said, I know enough to see there are flaws with the system, the question is there a way to improve the current system without re-installing the duct system. We are very close to where it needs to be and only need a small improvement to be "adequate". The reason I am remodeling this home is cost...cant afford new in the area I live.
thanks!
 

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It takes access to the ducts to do repairs.

You don't necessary need a new duct system as small changes can make a big difference.
 
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Discussion Starter #13
Fix the end taps.
I’m not sure how you want to bandaid a duct system that’s already a mess. Nothing to really bandaid there.
not sure I understand... i think we can all agree the old system was not done properly. Are you saying there is not way to improve the system?
 

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You could create a scoop inside the supply to catch the air. Might help some. Move the end taps into the side of the supply. Not sure if that would work. Not conventional. Really might be best to start the whole process over.
 

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Discussion Starter #16
You could create a scoop inside the supply to catch the air. Might help some. Move the end taps into the side of the supply
Thanks Bayou...this is exactly the kind of suggestions I was looking for. I know its not done properly and hoping to give it a band aid to improve since its not far from doing its job in the hottest of summer.

thx again!
 

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Getting rid of the end taps as suggested, putting smooth metal elbows, and dampers together could make a huge difference.

There are good people here who will tell you to re-do everything properly when it's not their money and diy is not practical, I've been guilty of that too - do what you can to improve performance.

Pictures and info re: actual duct sizes may be helpful. You could have an undersized return duct reducing pressure on the supply side - that's just one run and worth fixing. Could also have inefficient filter area for a 5 ton.
 

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To get our directions in sync lets say the top of your drawing is N.



You have a lack of air flow to the area and not cooling capacity, so the way i see it a plenum take off needs to be added to the S side to flow air to this problem area and completely close off the present 90 on the W side. ie move that W side 90 to the plenum and that would also shorten that run considerably.




Edit: Edit:
 

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Discussion Starter #19
I know there are problems areas throughout but, without question, my biggest issue is the initial 90 degree arm is not getting nearly enough air and naturally all the air is going straight. That said, does anyone have suggestions on how to divert more air to the intitial 90 degree arm? ....even if it does not solve the myriad of other issues?

Regarding the end caps, are you referring to the location the duct enters the plenum? if so, the drawing is not accurate in that they are towards the top of the plenum but definitely coming out of the side about 8-12" down from top of plenum. If that is something else, sorry!

thanks!
 

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I’ve never bought or used one of these before. But this is the principle I’m getting at. This would catch the air as it goes by and direct to your problem area. We’ve always made something. Or when cutting out the area for the duct left a portion of the cut attached and created a scoop so to speak. Can’t tell you the last time I’ve done it. But not everyone has the funds to do everything right. This may suffice. Also if any of your ducts in your problem area branch off with a very short run sometimes that causes issues as well. The air just keeps going straight to the next register
 
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