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Old 06-29-2009, 02:16 AM   #1
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Return air duct sizing concern


I had a new HVAC system installed last year with I believe a 5 ton AC unit. The home is 2200sq ft. I have two return air ducts that are non-flex 10'' ducting. One is located pretty close to the unit, the other is way on the other end of the house. Both units whistle on and off when the AC or HEAT is on.

The AC does not cycle at all. It's almost impossible for it to cool the house it will just maintain the current temp.

Is my return ducting too small? How big should they be? Is 2 enough?

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Last edited by amdspitfire; 06-29-2009 at 10:27 PM. Reason: It's a 5ton not a 3.5!
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Old 06-29-2009, 07:45 AM   #2
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Return air duct sizing concern


2-10" are almost big enough for 2 tons.

A 12 and a 14" or 2-14" round return ducts. Plus you need the return grilles to be big enough.

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Old 06-29-2009, 11:19 AM   #3
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Return air duct sizing concern


Quote:
Originally Posted by beenthere View Post
2-10" are almost big enough for 2 tons.

A 12 and a 14" or 2-14" round return ducts. Plus you need the return grilles to be big enough.
Should I stick to the metal piping and not flex?

Is this good? Will the "silent" ducts help for return ducts?

http://americanhvacparts.com/Merchan...xibleinsulated

Last edited by amdspitfire; 06-29-2009 at 11:40 AM.
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Old 06-29-2009, 12:17 PM   #4
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Return air duct sizing concern


Do I need something like this "return air can" against the ceiling, then to an elbow then duct?
http://www.theductshop.com/shop/2525...urn-p-297.html

Last edited by amdspitfire; 06-29-2009 at 01:36 PM.
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Old 06-29-2009, 04:02 PM   #5
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Return air duct sizing concern


Can you fit a 14" flexduct where your existing 10" aluminum duct is? If so, use 2 of these. Flex duct has more resistance to airflow than smooth aluminum but 2 14" returns should be sufficient.

This may or may not improve your cooling performance but should get rid of the whistling and allow the blower to work within its design specs.
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Old 06-29-2009, 04:46 PM   #6
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Return air duct sizing concern


Quote:
Originally Posted by sktn77a View Post
Can you fit a 14" flexduct where your existing 10" aluminum duct is? If so, use 2 of these. Flex duct has more resistance to airflow than smooth aluminum but 2 14" returns should be sufficient.

This may or may not improve your cooling performance but should get rid of the whistling and allow the blower to work within its design specs.
Yes, there is a good amount of room in the attic to fit bigger ductwork.
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Old 06-29-2009, 06:36 PM   #7
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Return air duct sizing concern


Something simular to that return can will help.
BUt, get it insulated. It helps to keep noise down.
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Old 06-29-2009, 06:36 PM   #8
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Return air duct sizing concern


You can use metal or flex.Either one will be find. Flex won't transmition noise as much as metal.
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Old 06-29-2009, 10:29 PM   #9
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Return air duct sizing concern


So it's a 5ton unit not 3.5 like I originally thought. Theres two 11-12inch return air ducts right now.

What size should I take it up to based on this new info?
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Old 06-29-2009, 10:33 PM   #10
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Return air duct sizing concern


2-14"

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