View Full Version : Size requirement for grille
pdormont
Jul 17, 2008, 08:59 AM
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
Jul 17, 2008, 03:18 PM
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
Jul 17, 2008, 05:20 PM
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
Jul 17, 2008, 05:57 PM
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.