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Insulating Cold Air Returns

 
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Old 12-31-2018, 01:26 AM   #1
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Insulating Cold Air Returns


Hey Guys,

Iím in the process of finishing my basement and before I hang drywall I am going to be installing with mineral wool insulation.

My question is what the best practice is when the joist bays are being used as cold air return. I have two joist bays in the hallway off the main rec room that are essentially straight runs up into two of the second floor bedrooms.

Thanks
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Old 12-31-2018, 02:59 AM   #2
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Re: Insulating Cold Air Returns


if you are going to insulate a joist bay to use as a cold air return, imo, you will need to isolate the return from the insulation to:

1) cut down on the coefficient of friction

2) eliminate any possible noise/whistling

3) eliminate any bits of insulation getting sucked into the system


i've seen insulation at the top of the return & bottom.

not sure if there is a right way. hvac guys chime in here.

also above or below, another way is to install a rectangular duct.

if no duct used the bay was sprayed with a heavy coat of paint to smooth it out, reference #1 & #2 above.

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Old 12-31-2018, 08:29 AM   #3
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Re: Insulating Cold Air Returns


If they are entirely in conditioned space now that the basement is getting finished, I don't see a reason to insulate them. Possibly smooth them out as Griz mentioned. We have to line them in metal here now.
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Old 12-31-2018, 01:20 PM   #4
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Re: Insulating Cold Air Returns


Quote:
Originally Posted by griz View Post
if you are going to insulate a joist bay to use as a cold air return, imo, you will need to isolate the return from the insulation to:



1) cut down on the coefficient of friction



2) eliminate any possible noise/whistling



3) eliminate any bits of insulation getting sucked into the system





i've seen insulation at the top of the return & bottom.



not sure if there is a right way. hvac guys chime in here.



also above or below, another way is to install a rectangular duct.



if no duct used the bay was sprayed with a heavy coat of paint to smooth it out, reference #1 & #2 above.


Thatís what I figured. A lot of work to box it in for just some sound proofing
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Old 12-31-2018, 01:21 PM   #5
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Re: Insulating Cold Air Returns


Quote:
Originally Posted by Golden view View Post
If they are entirely in conditioned space now that the basement is getting finished, I don't see a reason to insulate them. Possibly smooth them out as Griz mentioned. We have to line them in metal here now.


Itís always been conditioned space. Referring to insulation for sounds dampening
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Old 12-31-2018, 05:28 PM   #6
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Re: Insulating Cold Air Returns


Joist bays can not be used as returns at least based off any modern code

Insulation can be used for soundproofing but more importantly to help stop condensation issues - if you have no worries about that then no worries. If not insulation depends on the ducts being used & there are a ton of threads on here about that. Best thing though is make sure all those ducts are sealed good
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Old 12-31-2018, 05:33 PM   #7
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Re: Insulating Cold Air Returns


Quote:
Originally Posted by SLSTech View Post
Joist bays can not be used as returns at least based off any modern code

Insulation can be used for soundproofing but more importantly to help stop condensation issues - if you have no worries about that then no worries. If not insulation depends on the ducts being used & there are a ton of threads on here about that. Best thing though is make sure all those ducts are sealed good


Itís how all the cold air returns in everyone house I have every worked on have been. From $300,000 spec homes up to 2mil customs. Plastic pan in unfinished basements and just drywall on both sides of a wall for the rest
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Old 12-31-2018, 07:19 PM   #8
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Re: Insulating Cold Air Returns


Don't put insulation in it, it just turns into a dust magnet and you can't really blow it out in the future.

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Old 01-04-2019, 12:18 AM   #9
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Re: Insulating Cold Air Returns


Thanks for all the advice.

I ended up making a box of drywall so to speak so that I could insulate the bottom on the joist bay without having insulation in the cold air return.

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