Re: 3/4" Thermostatic valve fed by 3/4 hot and 1/2 cold ?
Posted by Kirk Ellis on May 07, 2002 at 17:04:38:
In response to Re: 3/4" Thermostatic valve fed by 3/4 hot and 1/2 cold ?
: : I'm putting in a whirlpool tub and want to improve the fill rate since it takes 66 gals. Since you use twice and much hot as cold in filling a bath, I'm planning on running a new 3/4" copper hot supply but keeping the existing 1/2" copper cold. I'd run the 3/4 hot right into the valve but use an adapter to fit the 1/2 cold into the valve.

: : Is the thermostatic mixing valve going to work this way ? I've had different opinions where some people think the valve will not be able to compensate for the different volumes of hot and cold. None of them plumbers, though.

: Kirk,
: In these cases, I like to run 3/4" to both the hot and the cold. The larger pipes are quieter when filling. The cost difference between 1/2" and 3/4" is not even worth mentioning. When I use Roman tub valves, the 3/4" kind by Grohe, I use mini-resters for water hammer.

Terry & hj,

Thanks for the info. Whether there will be enough cold to run the full volume of hot is what I see as the problem. I don't know that the cold will be a limiting factor, if the ratio of hot to cold is the 2-1 that I've read for bath water. I guess it depends how hot I keep my water heater -- the hotter the hot, the more cold will be needed for a 105 degree bath, right ?

It is actually the Grohe 3/4 valve that I am using. Since this is an existing bath with 1/2" hot and cold already running to it, I didn't want to have to run a new 3/4 line for cold. It isn't the cost of material, it is having to Tee into the 3/4" cold, leaving me with another possible leak point. I figure if I run out of time on the weekend when I make my changes to the copper piping, then as long as I haven't disturbed the cold, I can just turn off the supply into the hot water heater and I can turn the main back on to have at least cold water throughout the house.

How about if I install shut-off valves below the tub where I can access them through the apron, and run the 3/4 pipe 3 feet from both those shut-off valves to the Grohe thermostatic valve ? Would that allow the cold to equalize volume with the hot before they hit the Grohe ? Aren't the shut-off valves a good idea in any case ? The Grohe valves and trim will be mounted in the wall at about 45 inches height. The spout will actually be a Kohler Laminar Flow Ceiling Mount K-923 -- it looks really unusual and leaves me a clear tub deck :D

On the mini-arrestor issue, where should they go ?
Would I use Tees rather than elbows to go from vertical to horizontal into the Grohe valve, with the arrestors standing up ?

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