# Hey Ed, What Does Friction Rate Really Stand For?

In This Edition of “Hey Ed,” Ed Discusses What Does Friction Rate Rally Stands For

Hey Ed, what does friction rate really stand for? Friction rate is a number on a duct wheel or duct slide ductulator, if you will, that represents pressure drop per 100 feet. In fact, it's backwards. Friction rate is really the rate of friction, and the duct wheels that we're accustomed to, or the duct slides we're accustomed to using, through a little bit of math allow us to determine what our pressure drop in that duct is per 100 feet. Most duct systems have a TEL or a total equivalent length that is much greater than 100 feet, and you look at a duct system that's 30 feet long and say, how could it be? Well, it's not actual length it's equivalent lengths or actual lengths plus equivalent lengths that give us effective lengths. So, a typical 30-foot duct system in a typical basement could easily have a TEL of 3 or 400 feet. If you don't know what I'm talking about, I strongly recommend that you take one of our duct design classes whether it's a two-hour Zoom or come hang out for eight hours one day, and you'll walk out of that class with a better understanding of duct design and a good introduction to ACCA’s Manual D®. And that's the way I see it.

In This Edition of “Hey Ed,” Ed Discusses What Does Friction Rate Rally Stands For

Ed Janowiak is the Manager of HVAC Design Education at ACCA.

### Have a question you'd like to see Ed answer?

Send it on over by using the form below.

Posted In: Hey Ed, Technical Tips

Are you a homeowner or building manager?

BECOME AN ACCA MEMBER