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Old 10-31-2010, 07:43 PM  
nholmes8669
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It would help if you run 8" to the up stairs run. I would run the new hot air run in 8" and split it into too 6" up stairs, one to bath and one to main part. Run a 8"
return air and try to get the return hi if you can. Later paul
The only way to get any ducts upstairs is through a wall cavity so I think my choices are limited to an oval or rectangle duct for both the supply and return. I will do like you said and swap the 6" for the 8" for the existing duct to the second floor. Which is better, oval or rectangle? What is the biggest size that will fit in a wall cavity for each?


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Old 10-31-2010, 07:59 PM  
paul52446m
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A 6' oval pipe is only good for about 90 to 70 CFM of air. 6 rd is 110 CFM
8" rd is 225 CFM paul



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Old 11-03-2010, 05:57 AM  
nholmes8669
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A 6' oval pipe is only good for about 90 to 70 CFM of air. 6 rd is 110 CFM
8" rd is 225 CFM paul
So would it be better to go with a rectangle duct then? Like a 10x3.5 or 12x3.5 to get it upstairs?
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Old 11-03-2010, 04:07 PM  
paul52446m
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Thats a lot better than oval. 10x3.5 is good for 120CFM
12x3.5 would be about 150CFM
If heat can not go back up the studded space, just use that space for return air. Return air has to be larger that hot air to move the same amount of air.
Later Paul

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