What height is terminal velosity happen in drainage systems?

Question

What height is terminal velosity happen in drainage systems?

Answer 1

The rule of thumb for an interior drainage system is a terminal velocity of 10-15 fps is achieved within 10-15 ft from the point of entry.  It isn't how high the stack is, it's how far *below* the point of entry terminal velocity is achieved.

An equation for figuring the exact distance (also known as the terminal length) is based on flow rate and diameter and can be found here:

http://xnet.rrc.mb.ca/rcharney/interior....