I’m remodeling my bathroom including an entire shower rebuild so all the plumbing in the bath will be redone as the existing piping is old corroded galvanized.

I have a question related to the shower thermostatic valve.

The valve is a Porcher RP540 (I’m guessing it is identical to the American Standard Model: R540) with ¾ connections. As the shower will only have a single 2.5 gpm showerhead, ¾ pipe from supply to the shower valve and from valve to showerhead seems to be overkill.

My main concern is the volume of water in the pipes and the time for the hot water to reach the showerhead when the water in the pipes is cold (actually if my calcs are correct – the difference in volume of “standing” cold water in the approx 12’ run from the “supply” to the shower between a 3/4 and 1/2 pipe is about a quart or 4 secs of flow at 2.5 gpm). I do currently have a Lang recirculating pump on a timer under the sink nearest the shower – that has been a big help in warm-up time and water waste.

I don’t think pressure loss would be an issue with 2.5 gpm flow. (I’m not building a carwash as some of the newer showers appear to me)

• Did I goof in getting a valve with ¾ connections? (I bought it because I liked the porcher trim).
• Am I ok using ½ copper from the supply (approx 9 feet of pipe) and from thermo valve to shower head (3’) in this situation?

Thanks

Bob