ABC's Of Custom Shower Design Although installing a custom shower involves several tasks, they're just not that difficult, that is, if you keep some basic rules in mind. Following are the ABC's of custom showers as compiled by the GROHE Technical Service team: How Many Shower Outlets | The Valve | The Drain | Hot Water Volume Controls | Body Sprays | Valve Outlets Positioning Guide for Custom Shower Components This is simply a matter of arithmetic. The sum total flow rate of all shower outlets (shower heads, hand showers, or body sprays) combined cannot exceed the maximum flow rate of the thermostatic temperature control valve at the given water pressure. Exceeding the capacity of the valve will only lower the overall performance of the custom shower, and thereby lower your satisfaction. For example, all GROHE shower products are restricted to a maximum of 2.5 gpm at 80 psi. Five shower outlets would have a flow rate of 12.5 gpm (5 x 2.5 gpm). The Grohtherm 34 908 has a flow rate of 18 gpm at 45 psi. Obviously, this GROHE thermostatic temperature control valve would do the job. Notes on Shower Outlets TOP It should always be a thermostatic temperature control valve, and preferably a 3/4” thermostat valve. We recommend the GROHE Grohtherm 34 908 or the Grohtemp 34 902 which can be used with a variety of trim designs and finishes (trim sold separately). These valves will flow enough water to satisfy most needs, but critically important, a thermostat valve will control the temperature automatically as well. Temperature control in a custom shower is much more than a performance consideration, it is a safety consideration. A two handle valve system will flow more water, but without any constant, practical or safe temperature control at all! Remember, 1/2” supplies plumbed into a 3/4” valve will still increase water flow. (In this situation, a 3/4” valve will not perform at full capacity but will still flow more than a 1/2” valve.) It is not necessary to have 3/4” supplies to use a 3/4” valve, though when this is an option it is preferred. TOP Always determine the drain capacity. Two Grohtherm 34 908 valves can flow 36 gpm or more when combined (depending on pressure). That means that in 5 minutes you could have 180 gallons of water waiting to go somewhere! Will the drain empty the shower pan (floor) fast enough? Two 2” drains or one 3” drain is recommended, especially when an accessible shower pan is installed. (Drain capacity assumes proper venting.) TOP Remember the bigger the custom shower, the more hot water that will be required. A ten-outlet custom shower is hardly worth the effort and expense if there is nothing but cold water after two to three minutes. A 50 gallon water heater will supply a four-outlet custom shower for approximately 8 minutes (assuming shower heads are restricted and all are turned on for the entire duration)...is that enough for you? For best overall performance, consider a 100 gallon water heater as a minimum. TOP Custom showers are generally designed with separate on/off (volume) controls for each outlet or bank of outlets - typically, one volume control for the shower head, one for the hand shower, and one for three body sprays. (OOPS! There is no typical in a –custom” shower.) Volume controls, of course, have their own flow rates. We recommend using 3/4” volume controls throughout the system...GROHE 3/4” volume controls flow 16 gpm at 45 psi. If cost is a concern, 1/2” volume controls can be used, however, the flow rate is reduced to 8 gpm at 45 psi. Remember, the combined flow rates of the outlets cannot exceed the volume control flow rate without a reduction in performance. TOP Any configuration of two or more body sprays requires that they be plumbed with a pressure balancing loop ( see illustration ). This technique insures that each outlet delivers the same spray volume and temperature. TOP GROHE thermostatic temperature control valves are designed with two mixed water outlets. In a shower-only system (this includes multiple-head systems), the bottom outlet should be plugged. If a tub filler is part of the system, plug the top outlet and install a Twin Ell on the diverter tub spout to supply the shower outlets. (A Twin Ell is not required on some GROHE 1/2” thermostat valves.) Using both outlets simultaneously can cause inconsistency in temperature.