Duct/Grille Sizing Question


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Old 03-05-13, 12:48 PM
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Duct/Grille Sizing Question

I want to install a “stand alone” (not connected to HVAC system) whole house air cleaner for my 4000 square foot home. The unit has 675 cfm capability, with a 10 inch return entry and 8 inch supply exit. I will have one return duct pulling air from the upstairs and one supply duct supply air downstairs. Here are the duct and grill sizes I was thinking of using....if anyone has any thoughts, I would appreciate it (not sure I’m doing this right):

1. 14x24 return grill (336 square inches; chosen based upon rule that need 2 square inches per cfm for return grill…although I won’t be using a filter so maybe I don’t need that much size).

2. 12 inch return duct (rated for up to 700 cfm) which will have to have reducer to fit the 10 inch entry port of the unit (not sure why the unit does not come with a 12 inch entry since 10 inch duct isn’t rated for that 675 cfm).

3
. 10 inch supply duct (which will need a reducer to fit onto the 8 inch supply exit on unit)

4. I’m not sure of what I need for the size of the supply diffuser. Same as return?

Any thoughts would be appreciated. Also not sure why the supply side is smaller than the return side on the unit (10 vs. 8). Thanks!
 
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Old 03-05-13, 01:07 PM
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How long are the duct runs?
 
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Old 03-05-13, 01:49 PM
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Return run will only be about 6 feet. Supply run will be longer at about 25 feet.
 
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Old 03-05-13, 07:00 PM
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Looks good to me. My only thought would be to keep the supply at 8 the whole way. But depending are what your looking for 10 could be fine
 
 

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