Let me know if this is the sort of info you're looking for, if it's too basic, or not inclusive enough. It's a rough first draft and can be edited as required:
The sort of where, what, and why of pressure-balanced versus thermostatic:
Pressure-balanced or thermostatic temperature control valves are code-required in bathroom plumbing because they eliminate potential scalding and cold water shocks that can occur in a shower.
If you are using the shower and a toilet is flushed, as the toilet uses cold water to refill the tank, the pressure in the cold water line drops a bit below what it was when just the shower was running. If you had a non-balancing valve, youd still get the same amount of hot water that you originally were getting, but with the drop in pressure in the cold water line youÂd have less cold water coming out of your shower head, creating a potential for scalding. Vice-versa, if someone turns on a hot-water faucet elsewhere in the house, the hot water pressure drops and you get a shower of mostly cold water.
A pressure-balanced shower valve is designed to compensate for changes in water pressure. It has a mechanism inside that moves with a change in water pressure to immediately balance the pressure of the hot- and cold-water inputs. These valves keep water temperature within a couple degrees of the initial setting. They do it by reducing water flow through either the hot or cold supply as needed. Because pressure balanced valves control the temp by reducing the flow of water through the valve, if your plumbing supply is already struggling to keep up with the three shower heads and nine body sprays that you have running in your shower, if a pressure balancing valve kicks in and chokes down the water supply to keep you from getting scalded you could end up with insufficient water flow out of the heads in a multiple shower head setup. When it comes to volume control, in terms of being able to turn on the water a little or a lot, for the most part pressure-balanced valves are full-on when water is flowing or full-off when the valve is closed. Flow-wise, think of them as having no middle ground.
Where flow and volume control are important, as in a shower that requires a high volume of water, a thermostatic valve may be the better choice. They also control the temperature, but they do not reduce the amount of water flowing through the valve in doing so. Thermostatic valves are also common with 3/4" inlets and outlets, so they can pass more water through the valve than a 1/2" pressure balancing valve.
Which should you choose?
In a larger multi-outlet master shower, while a 1/2" thermostatic valve may suffice, a 3/4" thermostatic valve might be the better choice. But it does depend on the design of your shower and the volume of water that can be passed through your houses supply lines. In a secondary bathroom, or in a basic master where you have only one head, or the common shower head/tub spout diverter valve, a 1/2" pressure balancing valve would be fine.
If you want individual control and wanted multiple valves controlling multiple heads, then you could use multiple 1/2" valves instead of one 3/4" valve and all would be just fine.
What do the controls on the valve actually control?
While it may vary, a pressure balanced valve is normally an "all in one" valve with only one thing you can adjustÂthe temperature. The valve usually just has one rotating control (lever or knob) where you turn the water on, and by rotating it you set the water to a certain temperature. Each time you turn the valve on youÂll have to set it to the same spot to set it to your desired temperature. For the most part you really donÂt control the volume, just the temperature. With the valve spun a little bit, you'll get 100% flow but it will be all cold water. With the valve spun all the way, youÂll get 100% flow, but it will be all hot water. Somewhere int eh middle youÂll find that Goldilocks "just right" temperature, and itÂll be atÂyou guessed itÂ100% flow. So with a pressure balancing valve, you control the temp, but when the valve is open, itÂs open.
A thermostatic valve can be all inclusive in terms of control (volume and temp) or just be temperature controlling. If itÂs just temperature controlling, you will need a separate control for volume or flow. Example, with an all inclusive youÂll have two "controllers" (knobs or levers) on the valve, one to set the temperature and a separate one to set the volume. In this case you can set the temp as you like it, then use the volume control lever to have just a trickle of Goldilocks water come out of the valve, or you can open it up and have full flow of Goldilocks water coming out of the valve. You can leave the temp where you like it when you turn the volume off after youÂre done showering. The next time you shower, turn the volume on, the temperature is already set. Some thermostatic valves are just temperature valves with no volume control. YouÂll need another valve/control to set the volume. Read the product description carefully to see what you're getting.
What size valve should I get?
Yes, valves actually come in different sizes. The size refers to the size of the inlet/outlet nipples on the valve. For a basic shower, a 1/2" valve will suffice. For a larger multi-head arrangement, a 3/4" valve would be better. Realize that youÂll need a water heater that can supply the volume of heated water you want coming out of the heads, so donÂt forget that when you build or remodel. Also realize that if youÂre remodeling and have 1/2" copper running to your shower, capping 1/2" copper supply tubing with a 3/4" valve provide you with much benefit as the 1/2" tubing is the limiting factor. You can, however, cap 3/4" supply tubing with a 1/2" valve or a 3/4" valve.
Is one better than another?
Thermostatic valves are "better" in that with them you can control both volume of flow and temperature, so you have more control, and they hold the temperature to a closer standard (+/- 1 degree). They also perform better if you are running multiple outlets in the shower, as they do not choke down the amount of water in order to control the temperature. But you pay for that added flow and added control. Pressure balancing valves can be had for about $100-$200, thermostatic valves can be twice that amount. And more.
Will I suffer with a pressure-balancing valve?
For what itÂs worth, when I built my house over 10 years ago I put pressure-balancing valves in my own house. While I have two outlets in my shower (sliding bar mounted hand-held on the wall and an overhead 12" rain shower head on the ceiling), I have a two separate pressure-balancing valves, one valve for each head. With both heads going in the shower, I notice no loss of flow in the shower when the toilet is flushed and the sink faucet is turned on simultaneously. I also notice no change in temperature. So they work for me.
If you are remodeling, if you have your existing sink running and you flush the toilet and notice a drop in volume coming out of the sink, then a thermostatic valve might be the better choice even if you're not having a multi-head setup installed.
If, as part of the remodel, you plan on running new supply lines through your house to the new bath, then properly sized runs will take care of that flow restriction and you can probably do a pressure balancing valve instead of a thermostatic.
So in a house with tricky plumbing, or with a restricted water supply, or with multiple outlets running off of one supply valve, a thermostatic valve might be the safer choice.
Mongo
Q
picture
Q