Q: How large does a return air grill need to be? I have 1 right under my unit that is 7″ x 32″. Is that enough?
The return size depends on the capacity of the cooling system, length of return run and size of the return chase. As a basic rule of thumb you can multiply the width by the height of the return grill and then divide by 144 to determine if your return GRILL opening is within range of the total system tonnage.
Example: 12 x 24 return grill equals 288 square inches, divided by 144 equals 2 which represents about 2 tons.
Example: If you have a return chase or return duct over 12 feet long, then divide by 150 instead of 144. 7 x 32= 224 divided by 144 is approximately 1.5 tons cooling.