Two demand loads combine on a main: branch A carries 40 WSFU and branch B carries 60 WSFU. If the Hunter demand chart converts 100 WSFU (predominantly flush tanks) to about 44 gpm, what design flow sizes the main?

Explanation

You add the fixture units first, 40 + 60 = 100 WSFU, then convert the combined total to gpm on the demand curve, giving about 44 gpm. You must never convert each branch to gpm and add the flows, because the Hunter curve already accounts for the low probability of simultaneous use, and adding gpm overstates demand.