What is a “B” dimension?
The “B” dimension is similar to the “A” dimension except it is used what we have two pipe steam systems. The “B” dimension as also calculated differently. We are still interested in the distance from the NWL to the lowest steam carrying main. Instead of 28″, it is now 30″ per pound of steam in a system. If the system were operating on 2 psi we would need to have a vertical distance from the NWL to the lowest point on the steam carrying main of 60″ or 5′. Since most basements do not allow that kind of height, we use traps with gravity return or pumped returns.
