Providing answers to your plumbing, piping, fire protection and hydronics questions.

Not Enough Water to go Around writes:
I am the service manager/technician for a plumbing contractor and was asked to look at a new house, which features eight bathrooms, a kitchen and laundry. The residents have a problem in the master bath regarding flow rates. If they turn everything on in the master shower, there is not enough water to go around.

The master shower features: three thermostatic mixing valves (3/4 inch); six wall valves (3/4 inch) that control the water flow to the different shower heads or body sprays; an overhead rain shower; a regular wall-mounted shower head; a wall-mounted hand shower; and 12 body sprays.

There is a 1-inch copper cold water feed line to this bathroom and a 3/4-inch copper hot water line. The water meter is 1-1/2 inches, and the main to the house is a 1-1/4-inch copper line. Incoming city water pressure is 65 psi, but sometimes it drops to 55 psi.

Any advice?

Julius Ballanco responds:
Sure, that is an easy one. The water piping to the master bath is undersized. You are trying to flow more water than the piping system is designed to flow. First, thermostatic mixing valves require a minimum flowing pressure of 20 psi. If you do not meet this pressure demand, the valve will not operate properly.

It appears that you have three showerheads, each of which is rated for 2.5 gpm. That means there is a demand of 7.5 gpm through the three showerheads. You have an additional 12 body sprays, which flow anywhere between 1 gpm and 2.5 gpm. Assuming the higher flow, that would mean that 12 body sprays are flowing 30 gpm. Even at 1 gpm, that is an additional 12 gpm - making the total flow between 19.5 and 37.5 gpm.

You did not provide the temperature of the hot and cold water, so let's assume that there is an even use (50%-50%) of hot and cold water (which probably is not accurate, as typically more hot water is required). That means you are trying to flow between 9.75 and 18.75 gpm through a 3/4-inch copper tube.

The Code allows you to flow 8 gpm through a 3/4-inch hot water line. The pressure loss at that flow rate would be 5 psi per 100 feet of pipe. At 18.75 gpm, you are trying to flow water at a velocity of 11.8 feet per second. The pressure loss would be 29 psi per 100 feet. Hence, there is not enough pressure to flow that much water. Even if there was, it would eat away the copper within a two-year period of time. Furthermore, the thermostatic mixing shower valves are rated for 2.5 gpm. If you flow more water than that through them, you lose additional pressure.

You simply have a sizing and pressure problem. Try having a shower with a single showerhead flowing 2.5 gpm so that you conserve water, or increase the size of the hot and cold water line to 1-1/4 inches.

Different Piping Materials

Emo Benoit (Veolia Water Asia, Shanghai, P.R. China) writes:
What is the main difference between PP-R, PEX, CPVC, and aluminum-reinforced PVC piping materials? Do you have some length guidelines for fixing the small pipes to wall?

Julius Ballanco responds:
They are all different plastics. PEX is considered flexible; PP is considered semi-flexible; CPVC and PVC are rigid pipe. As for hanger requirements, rigid plastic pipe has a spacing requirement of four feet for hangers. Flexible plastic pipe has a spacing requirement of 32 inches.

California AB1953 - Low Lead in Brass Valves/Fittings

Alvin Markus (PVF Engineering; piping industry consultant) writes:
California bill AB1953 is to take effect Jan. 1, 2010, and it limits lead in brass valves, fittings or plumbing (used in drinking water) to a maximum of 0.250%. Which brass alloys are recommended for brass-threaded valves for forged components and cast components? Please advise.

Julius Ballanco responds:
California had no recommendation. The copper alloy industry has not provided any specific recommendation. Every manufacturer is currently experimenting with different qualities of brass. It has been suggested that bismuth may replace lead. However, there isn't enough bismuth in the world to replace all of the lead in brass. It is an interesting time for the brass industry.