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Old 05-17-2011, 09:56 AM   #1
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Air conditioning duct work


Hi. I need some advice. I bought a new heat pump last year. It's s 3 ton unit. It doesn't cool my house below 78 degrees. I had someone look at it. They are telling me 90% of my home cooling problems is the duct work. He said he would remove the trunk lines and rectangular shaped duct work and build a 4ft long box off the air carrier and run the flex tubing diretcly to the box. I think I can do this myself, but was wondering the complete deminsions. Height, Length, and Width? Any advice would be great.

Thanks,

Jeff

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Old 05-17-2011, 03:39 PM   #2
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What size is the opening in the air handler.

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Old 05-17-2011, 03:46 PM   #3
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The opening is 11.5 inches wide, and 13 inches high. Should I build a long trunk to fit all 9 flex tubes? Any help would be great.
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Old 05-17-2011, 03:51 PM   #4
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I prefer to build the box a bit wider then the opening. A 4' long trunk is ok, but longer is better. How long will the flex runs be to the box? Long flex runs tend to reduce air flow.
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Old 05-17-2011, 05:41 PM   #5
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I can build the box longer no problem. I don't have any idea how wide or tall to build it. Some of my flex will be 15ft. The builder put the air carrier toward the back of my home in the attic. This makes the living room and kitchen hot. Very little air flow out of vents. Do you have any suggestions to increase air flow for the front on my home as well?
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Old 05-17-2011, 06:42 PM   #6
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Quote:
Originally Posted by js.craig View Post
I can build the box longer no problem. I don't have any idea how wide or tall to build it. Some of my flex will be 15ft. The builder put the air carrier toward the back of my home in the attic. This makes the living room and kitchen hot. Very little air flow out of vents. Do you have any suggestions to increase air flow for the front on my home as well?

Can you take some pics and post them? Proper duct take off positioning on the plenum box is vital to air flow as well. You can also add dampers on the plenum right at the duct take off so if one or more rooms are receiving possibly more than adequate air and/or you simply don't need so much to said room(s) than you can close those dampers to produce more air flow through the other ducts.

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Old 05-17-2011, 07:09 PM   #7
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Transition from the air handler's opening to a 12X18, make it 6 to 8 foot long. The shorter the flex, the better. No harm in making it 12 foot long either.

Next, what size is your return?
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Old 05-17-2011, 07:32 PM   #8
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8" flex runs?
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Old 05-17-2011, 09:03 PM   #9
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8" flex runs?

?????
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Old 05-17-2011, 09:56 PM   #10
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Just wondering. Three tons and only 9 runs.
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Old 05-17-2011, 10:10 PM   #11
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Just wondering. Three tons and only 9 runs.

Surely your not impling that the supply runs could be too small.
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Old 05-18-2011, 12:42 AM   #12
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Im in the middle of doing a install in my home, i found this helpful

http://www.alabamahabitat.org/sustai...ct_Systems.pdf

Quote:
Size supply plenums to the flanged opening of the blower outlet,not to the extents of AHU cabinet
My opening was like 10x14 or something those lines, i made a transition to a 12x18 supply trunk

some pics

( keep in mind I am not a pro, this whole setup could be completely wrong and fubar, but it might give you a visual )






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Old 05-18-2011, 04:49 AM   #13
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Thats not a transition, thats a butt joint. Its a very turbulent joint, and generally should be avoided. A transition, would be when the duct angles out or in to the size of the next duck. If you redo yours, it will help with air flow.

By the pic, your first take off may or may not be far enough a way from the joint to allow the air to stabilize. I suggest you redo the butt joint to a transition.

The rest of your install judging by the pics is very clean looking.
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Old 05-18-2011, 08:04 AM   #14
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Originally Posted by beenthere View Post
Thats not a transition, thats a butt joint. Its a very turbulent joint, and generally should be avoided. A transition, would be when the duct angles out or in to the size of the next duck. If you redo yours, it will help with air flow.

By the pic, your first take off may or may not be far enough a way from the joint to allow the air to stabilize. I suggest you redo the butt joint to a transition.

The rest of your install judging by the pics is very clean looking.
Thank you for the suggestion beenthere, I will look into it.

If kept, will this just be a noisy joint with blowing air sounds?

And my first run off is 36" from end of AHU to the center of my first 8" run off, there is also another run off in the same location on the backside.


Also, is " Butt Joint " the proper term for it? My Google-Fu must be weak, I cant seem to find any information on the joint on my search.

Thanks.
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Old 05-18-2011, 08:40 AM   #15
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Butt joint more refers to carpentry. http://en.wikipedia.org/wiki/Butt_joint

I think what BT might mean is those boxes are butted together verus being transitioned from one to the other.

I don't think that tape is meant for air leaks. From what I understand it is mainly used for insulating commercial metal duct, on the insulation itself and not on the metal.

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