Valve Size and Selection
Whether you're gutting your current shower or planning a new construction in your bathroom, one of the most important considerations on your blueprints should be valve size and placement. When planning a shower design, your first step is choosing the applications you want. Whether it's Hangrohe's massive Raindance shower head or a mix of Kohler's WaterTile series, the features you select make your showering experience unique.
Once you select your features, what makes or breaks the shower's functionality is your valve sizing. When it comes to shower valve sizes you'll have the choice between ½" and ¾" 
connections. Most homes come with existing ½" pipe. By selecting ½" valves, you can save some money and hassle on your remodel project. However, ¾" valves will give you extra power and increase your flow rate. If you're looking at multiple or oversized shower heads or four or more shower functions ( shower heads, handshowers, or groups of bodysprays), ¾" valves will pack a punch and provide the water flow to power multiple functions simultaneously.
Let's break down a few possible remodels and project what valve sizes you might want to take in consideration.
Single Function Shower:
This is your run-of-the-mill shower head with a handle to control your temperature and turn your system on and off. Expect a peak demand of 2.5 gallons per minute (GPM). These systems will need ½" valve options. The Danze Parma, D500558BNT is a great example of your traditional single function shower.
Two Function Shower:
You can get a bit more creative in this set-up. With your standard shower head, you can add a handshower or up to three body sprays. Your total water demand will be between 2.5-3.0 GPM if you only are using one of your functions, but can be over 5.0 GPM if you're using both features simultaneously. If you only use one function at a time, ½" valves are more than sufficient. If you plan on using both at the same time and your home's pressure per square inch (PSI) rating on your water main is under 40, you might want to consider upgrading to a ¾" valve. A great example of a two function system is Showhouse by Moen's Waterhill, TS511BN.
Three Function Shower or Vertical Spa:
These systems will typically combine a shower head with a handshower and a group of body sprays. Some variations include multiple groups of sprays or more than one shower head. When all features are used simultaneously, your water demand can rise to over 8 GPM. A ¾" valve is highly recommended for these applications, especially if your home's water pressure is under 60 PSI. Having a tankless water heater for your home can help keep a consistent hot water flow throughout extended showers. Showhouse by Moen's Divine series vertical spa is a great example of a three function shower system requiring a ¾" system.
Custom Shower Systems:
Custom shower systems often have ceiling panels demanding a large draw of water or four or more shower functions. Often times these systems will use a network of volume control devices with one or more thermostatic valves. These systems can draw 10-20 GPM when in full operation and should always have ¾" plumbing connections. You might also want to consider a designated tankless hot water heater for the bathroom to compensate for higher hot water consumption. The WaterTile ceiling panel by Kohler is an excellent centerpiece for a custom-tiled walk in shower that would require ¾" valve options.
Valve size is an important consideration, but some of the other aspects to keep in mind include:
SAFETY
Temperature Limit Stops:
Often the showers we design need to be kid friendly. A simple way to ensure they don't get burned is select models that include a scald guard or limit stop. Most brands, including the budget friendly Danze and Price Pfister to the designer lines from Kohler and Showhouse by Moen include scald-guards as a standard feature.
Pressure or Thermostatic Balancing:
The showers of yesteryear would often have hot or cold water spikes when running appliances or flushing toilets in the house. Most models today come with pressure balancing mechanisms to minimize temperature spikes. Many of Hansgrohe's valves include a thermostatic balancing device, more accurate than the traditional pressure balancing upgrade. Hansgrohe's Solaris Handle and Valve trim is an example of their thermostatic balanced valves. It also functions as a volume control, temperature control, and diverter all in one unit.
Service Stops:
Purchasing valves with service stops included or upgrading to a model that includes them can save a lot of time and hassle both during your remodel project and after the fact with service. When available, upgrades will only cost an additional $10-$20 per valve and cost nothing additional for your plumber to install. Plumbers installing stops after the fact will charge for the part and the installation. Built in service stops act as an insurance plan; should you ever have a problem with your shower leaking, you can remove the decorative trim and shut off the water at the stop rather than turning off water to your entire house while waiting for a plumber.
Compatibility
If you're keeping your existing valves on the walls and just updating your trim, stay with the same manufacturers. Most manufactures have unique valve to handle fittings that are not compatible. You can mix and match different manufacturer's shower heads, handshowers, and bodysprays, but be careful for variations in finish, even in common colors like Brushed Nickel and Oil Rubbed Bronze.
If you currently have ¾" plumbing and are installing a simple shower system, a ½" valve is backwards compatible. You can purchase ½" to ¾" adapters at your local hardware store. If you have ½" plumbing and are looking to get into a three function or custom shower system consider consulting with a plumber and upgrading your source pipe from ½" to ¾" and purchase ¾" valves.
PRICE
If you're keeping to a budget, consider sticking to a simpler shower and ½" valves. Most manufacturers charge a premium for the larger valves. For less than $10.00 Hansgrohe allows an upgrade option from ½" to ¾" on some handles and their matching valves. So, if you need ¾" on a budget start your search here for volume controls and here for your thermostatic controls.
For versatility in your shower design, try building a custom Danze system. They provide the only diverter valve system that allows you to run three functions simultaneously. It provides a clean finish on your wall and minimizes the exposed handles. Start here to select a two handled thermostatic/volume control combo and then pick the matching diverter here. From there the sky's the limit; pick up to three shower heads, handshowers, or groups of bodysprays. Remember to check specification sheets and product descriptions to ensure your valves and packaged shower systems are the proper size and have all the safety features you'll require for your family. When picking your valves, start with the type of shower functions you want to install and then work backwards. Once you plan the finished shower, you can select the right sized valves that will breathe life into your new showering experience.
