[pdormont]

Need an interior grille to cover a fresh air intake in a bedroom. Capacity of fan venting the space is 450 CFM. How can I calculate the amount of open grille area needed to accommodate this?

[hvac1000]

How large is the duct? 16X20 or?


Use this formula


easy formula

2 x width x height x 80%

example 20x25 return air grille

2 x 20 x 25 = 1000

1000 x 80% = 800 cfm

Example

So, a 20 x 25 return air grille will provide 800 cfm's back to the unit.

[pdormont]

Need an interior grille to cover a fresh air intake in a bedroom. Capacity of fan venting the space is 450 CFM. How can I calculate the amount of open grille area needed to accommodate this?

Thanks! Does the 80 represent the % open area of the grille and does that need to be adjusted if, say, the grille is only 50% open?

[hvac1000]

The 80% is a ruff guess. The best way to do it is to find out the manufacturer of the grill go to there site and they will have a listing.