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Old 08-27-2008, 09:37 AM   #1
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Looking for a better cold air return.


This might be hard to visualize without a pic, but I am not at home.
Here goes.

I am finishing my basement and am putting insulation in the ceiling to provide some sound damping. Currently the cold air returns for the 1st floor bedrooms are just cut into the walls and then run between the floor joists, ceiling joist if you are in the basement. There is currently no ducting for the return the drywall on the ceiling will make up the bottom of the ducting.

So, I need to close the bottom of the return so I can add insulation below it. The question is do I need to use sheet metal cut it, bend it, and screw it into the studs, or can I just staple plastic to create the return.

Please say plastic.

Thanks,

Ben

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Old 08-27-2008, 01:20 PM   #2
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Looking for a better cold air return.


to use drywall as cover for return air duct is fine,... use insulation definite not good... use plastic may seems good but plastic is not strong enough and may have holes here or there ... so metal is the one to be used.... what the code say I am not sure... but that is what the books say ....

what's wrong with using metal... I don't know why you have an issue.... why do you need to blend it... I know you need to cut it... but why do you need to blend it.... there are 20 ways to cut metal and is really not a big deal....

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Old 08-27-2008, 01:37 PM   #3
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Looking for a better cold air return.


I don't think I explained the issue very well. I need to seal the bottom of the cold air return about half up the ceiling joist cavity so there is room for insulation between the cold air return and the ceiling which will be rock on resilient channel. Therefore I was thinking I need to bend the metal so I can screw in to the joist or staple plastic.
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Old 08-27-2008, 01:52 PM   #4
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Looking for a better cold air return.


such as sister a small 1x1 wood to the joist ...etc...bending is not easy I know... but using plastic I would not think it is code compliance although I am not sure... but if you have to bend the metal... may be it can still be done, you may need to hammer it against a 2x4 to make it blend 90 degree.... will just wear a strong glove and you should be fine...
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Old 08-27-2008, 03:20 PM   #5
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Looking for a better cold air return.


Thats a good idea about sistering. I have a ton of scrap 2x4 and a framing gun so shouldn't take to long. We are only talking about 4 joist bay and a run of about 5'. Thanks for the idea.
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Old 08-27-2008, 03:28 PM   #6
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Looking for a better cold air return.


Have you considered what impact reducing your return air flow will have?
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Old 08-28-2008, 12:41 PM   #7
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Looking for a better cold air return.


I think I should be ok. Currently the 2 bedrooms which will be effected have a total of three supplies fed by 5' ducts, so a supply area of around 60 sq in. The return ducts are 8" by a15" currently so 240 sq in. I will cut that in half and still have twice as much return to supply. I am under the impression you need to have at least the same amount of supply and return.

I am also adding a return in the basement.

I have some Hvac guys coming over tomorrow to do a 30 day check on a new AC, so I will run the plan by them also.
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Old 08-29-2008, 05:29 AM   #8
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Looking for a better cold air return.


You could use rigid foam insulation as the sound barrier only where the return ducts are. That would serve both concerns. You can still cover the returns as you described, and reduce any questions about the return sizing.

Return air is low pressure, low velocity air. Supply air is just the opposite. Surface area of the return is only one factor, or a result of the calculation.
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Old 08-29-2008, 03:05 PM   #9
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Looking for a better cold air return.


You could use a product called thermo-pan. Thats what we use for joists and headders around here. It is designed for what you are trying to do. It is a cardboard like product that has a foil on each side. Cuts easy and is marked with 1" lines both ways for easy measuring and bending. Can be bent over a stud and installed with staple gun. Ask the guys comming over ot sell you some. Should be fairly cheap.
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Old 08-29-2008, 08:02 PM   #10
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Looking for a better cold air return.


Quote:
Originally Posted by 8 Ball View Post
You could use rigid foam insulation as the sound barrier only where the return ducts are. That would serve both concerns. You can still cover the returns as you described, and reduce any questions about the return sizing.
Sounds like a great alternative!
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Old 08-31-2008, 02:42 PM   #11
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Looking for a better cold air return.


Thanks, we had to push the appt back until Tuesday, but I will ask them when they come over.

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