[Greenbuilding] Cold air return/s

Ron Cascio roncascio at verizon.net
Tue Jun 28 13:36:29 CDT 2011


" Because warm air is buoyant a single return should be located high. "

And place it where you believe the hot air will stratify, and/or can grab 
warm air that is generated by solar exposure or other heating systems like a 
woodstove.


Ron



----- Original Message ----- 
From: "Michael O'Brien" <obrien at hevanet.com>
To: "Green Building" <greenbuilding at lists.bioenergylists.org>
Sent: Tuesday, June 28, 2011 2:03 PM
Subject: Re: [Greenbuilding] Cold air return/s


> Hi, Larry--
>
> In theory the supply side and return side should have the same air flow.
>
> However, typically each room has at least one supply while the entire 
> house has one return so the system may be out of balance right there. And, 
> when doors are closed, individual rooms experience positive pressure while 
> the main house goes under negative pressure. The same is true for ductwork 
> that has air leaks in it--in an out-of-balance system, supply ducts will 
> leak more conditioned air while the return duct will pull in more attic 
> and garage air.
>
> An out-of-balance system may increase air leakage by increasing pressure 
> differences across the envelope, especially if no air sealing is done as 
> part of the upgrades you listed. Increased air leakage will contribute to 
> the house becoming too dry in winter, by increasing the loss of humidified 
> air and its replacement by cold dry outdoor air.
>
> So ideally the return should be able to "see" the whole supply side, with 
> no barriers to flow. That can be aided by installing transfer ducts on 
> rooms that need to be closed for privacy. Because warm air is buoyant a 
> single return should be located high.
>
> All in all, probably a good idea to invest in sealing the envelope and 
> ducts in unconditioned spaces in order to get a single return to function 
> properly.
>
> Please let us know your solution.
>
> Best,
>
> Mike O'Brien
>
>
> On Jun 26, 2011, at 12:15 PM, Myers, Larry A. wrote:
>
>> I am in the middle of a near total renovation of a 30 year old house 
>> (1600 sf, 3 BR, 2 Bath), that wasn't great energywise to start with. I am 
>> making some modest changes to save energy -- more insulation, triple pane 
>> windows, Energy Star roofing and appliances, etc.
>>
>> I have a reasonably efficient gas furnace/AC unit. My question: Is there 
>> an optimum place to site the cold air return? And is there any advantage 
>> to having two returns, or more? If so, where?
>>
>> Thank you.
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>
>
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