Shower Units: 3/4 in. valve & 1/2 in. NPT

[Rahul R.]

*Be advised, I have no deep knowledge of plumbing. We are in the process of building a new home. Currently, we are working on the bathroom design ahead of the rough-in inspection. We are looking at Kohler shower fittings (rainhead, regular showerhead, and handheld). These three outlets use a total of 6.5 gpm. The specs sheets say that the fittings have 1/2 in. NPT connection.

The question is whether it is possible to pair these fittings that use 1/2 in. NPTs with 3/4 in. thermostatic and volume control valves and pipes? Or are we required to use 1/2 in. thermo and volume valves? The 1/2 in. thermo valve available for these fittings has a listed 10.9 gpm rating. The individual 1/2 in. volume control valves have a flow rate of 10.0 gpm.

Thanks

 

[Jadnashua]

If you have 3/4" supply lines, given your situation, I'd opt for the 3/4" main valve. But, using the individual valves off of that with 1/2" inputs won't be a problem as each individually, can't use the volume of the 3/4" valve. Note that the copper institute design specs say to not exceed 5fps for hot water flow rate for maximum long-term reliability and to minimize noises. That volume would vary based on the pipe size. For 1/2" pipe, that equates to 4gpm; 3/4" pipe doubles that to 8gpm. While you can exceed that, IMHO (and the copper institute), you're asking for problems. For best tub filling and to minimize pressure drops from friction at higher flow with smaller lines, having more water than you need is ideal. Ever tried to run more than one sprinkler off of a hose with an adapter? Neither one usually works well...same idea with shower heads - you want more available so the restriction in the head causes the water to speed up, otherwise, it can dribble out sort of like a rain head verses a jet.