Shower Plumbing Move

[groundedchevy]

This weekend i'm I'm going to be ripping out our master bathroom shower and the wall that has the shower plumbing. The plumbing will be moved to the opposite wall. The current setup has a 3/4" cold water line with a tee going to 1/2" up to the valve and a 1/2" hot water line going up to the valve (I am unable to see the 3/4" hand off. As you can see from the pictures the hot water tank is very close the new and old plumbing. Would you recommend running 3/4" from the hot water tank and changing it to 1/2" right under the valve? I'm planning to install a Delta R22000 valve. I will have a shower head and a handheld that I would like to be able to power at the same time. I thought running the 3/4" from the hot water tank would make sure I have significant pressure to both shower heads.

 

[Jadnashua]

A shower head is limited to a maximum of 2.5gpm, and most output less. As long as your supply is capable of at least and preferably more than the outlets, it will maintain the pressure. It's when the outlet openings can't be fully satisfied is when you'll notice a loss in velocity.

A typical 1/2" shower valve is rated at about 6gpm. But, consider that the copper institute (the industry guidelines) calls for a maximum velocity in a hot water pipe of 5fps, on a 1/2" copper pipe, that equals 4gpm. On a 3/4" pipe, it doubles to 8gpm. While the smaller pipe can produce a higher flow rate, that causes the dynamic pressure available to decrease because of the increased friction. Over a short distance, it isn't huge, but it is there and measurable.

So, depending on the incoming cold water temperature, and therefore the relative mix of hot and cold to get to your desired outlet temp, it might work fine in the summer when the cold is warmer and therefore you use more of it to temper the hot, but in the winter, you'll be using much more hot in the mix to get the same temperature outlet, and you might be pushing the limits on velocity (probably not on volume).

I'd consider running the 3/4" and reducing it at the valve. FWIW, on the cold supply, it can run faster and not cause problems, so 1/2" will be fine. If you decided you wanted more that two heads running, IMHO, you'd probably want 3/4" valve and lines going to it.

 

[Sponsor]

 

[hj]

Regardless of the number of heads, or pipe size feeding the valve, your volume will be limited to what is available through the valve, and the ports inside the valves will be about 1/4" diameter, so 1/2" copper will be more than adequate.