Return Air Velocty

[Gary Swanson]

What is a good rule of thumb for designing return air ductwork. Is there a recommended maximum velocity and static pressure?

[George2]

What is a good rule of thumb for designing return air ductwork. Is there a recommended maximum velocity and static pressure?

First, I locate where the returns are going, then I size the ductwork accordingly. If I'm working with a 4 ton (1,600 cfm) blower, I'll design at least 1,800 cfm of return air grilles.

[rundawg]

What is a good rule of thumb for designing return air ductwork. Is there a recommended maximum velocity and static pressure?

Manual D says the Maximum Return side FPM for Flex duct should be:

Return Grill face velocity - 500 fpm

Filter Grill face velocity - 300 fpm

Trunk and Branch Ducts - 700 fpm

Conservative velocities:

Trunk and Branch Ducts - 600 fpm

Return and Filter Grill stay the same as listed above.