Separate Bath and Shower Mixing Valves

My latest idea, as I just posted to Terry Love's Blog:

I am really liking separate valves for tub and shower and hoping I can get the plumber to do it. Especially with a valve like Delta 1700, my plumber's favorite, it can't be too low when you're taking a shower because you have to reach underneath the center of control to control the all important volume, so mounting it below 48 inches on center is lousy when your taking a shower, but obviously makes the valve unreachable if you're taking a bath.

AND, I think a Moentrol single handle V/T control (it appears no one else makes a control like this anymore) makes the best sense for a tub. My plumber seems not to like this valve and strongly prefer Delta. But let me explain why the Moentrol is perfect for bathtub. During one bathing session, you may need to adjust the volume and temperature in many different ways. You start out full force hot or nearly so. Then if you overshoot, you run colder water for awhile at some intermediate volume. Then you run a trickle hot during the bath itself. If it gets too hot you may need another blast of medium cold, and so on. A single handle valve is perfect for making all these changes on the fly, even if it doesn't allow finer control of pressure, and the "memory" aspect of temperature control isn't that great.

OTOH, the 1700 with dual handles is perfect for a shower. For a shower, and for especially for one person, you basically can set the temperature control once and forget it. Just turn on and off and up and down the volume as needed with the larger volume handle.

So this gives another reason for having dual valves. The temperature dynamics are completely different. For shower you just want constant temperature, for bath you need to vary the temperature all over the place. And if you take a bath, you need to remember to re-set the temperature next time you take a shower. And it might be good to have different kinds of controls as well, with dual handle control for shower and single handle for bath, as I have just described.

Finally, there's a third good reason for separate mixing valves. No surprises. This is especially true with spout type diverter. I can't count the number of times I've pulled the spout diverter and it doesn't go as expected--wrong spray head selected, wrong spray option, too much pressure, etc. If you have a fixed control (or another kind of diverter) you don't get those kinds of surprises. You just ramp up the volume from zero. But even with an in-wall diverter, you can still have the surprises coming from forgetting to check which way the diverter is turned.