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Hot Water Recipe


When using commercial water heaters, it is dangerous and sometimes against code, to supply hot water at F180° directly to the fixtures in your facility. All hot water for general use needs to be mixed down to F140°. Any of the major water heating equipment manufactures can provide suggestions for the most effective method of delivering safe hot water to your particular situation. Exception: Waterwerks Showers are equipped with integral thermostatic water controllers that do not require pre-mixed hot water. These mixing valves are designed with a safety feature that allows the user to pre-set a maximum temperature that cannot be exceeded.

Beautiful bathtubTypical Hot Water Recommendations for Waterwerks Showers:

Based on F104° water temperatures at the showerhead with all showerheads in operation. It should be noted that service protocols vary significantly from one spa location to another. In most cases, all available showerheads are not running the entire time the service is being conducted.

  • Blast Vichy Shower - Seven Headed Vichy Shower - 10.5 gpm (max) Recommend 105 to 125 gallons of F104° water per hour
  • Cascade Vichy Shower – Five Headed Vichy Shower - 7.5 gpm (max)
    Recommend 80 to 100 gallons of F104° water per hour
  • Typhoon Vichy Shower - Seven Headed Vichy Shower - 10.5 gpm (max)
    Recommend 105 to 125 gallons of F104° water per hour
  • Torrent Vichy Shower - Seven Headed Vichy Shower - 10.5 gpm (max)
    Recommend 105 to 125 gallons of F104° water per hour

A primary concern for any spa making the commitment to offer quality hydrotherapy treatments is the consistent availability of sufficient hot water. In fact, failure to provide a sufficient hot water supply is one of the most frequent and costly mistakes made in the planning of hydrotherapy rooms. By providing answers to the following questions, you will be able to present to your plumber contractor, architect or mechanical engineer a clear picture to ensure the accurate prediction of what your individual hot water requirements will be in order to facilitate water heater sizing.

Questions you need to ask before you install your hydrotherapy equipment.

How Hot?
  • How hot will the water typically be at each fixture in use?
  • How hot will you have your hot water supply?
  • What is the temperature of the water that supplies the hot water heater(s)?
  • What is the most economical energy source available to your particular project (natural gas, propane, electrical, etc.?)
  • How much space will be available to accommodate water heating equipment?
How Much?
  • How much water does each fixture consume? Each fixture will have a maximum flow rated in gallons per minute (gpm). If you can’t find it printed on the fixture it should be indicated in the manual or instructions. If you are still unsure, consult the manufacturer.
  • How many minutes will each fixture be running per hour? For example; a shampoo bowl might be used twice in an hour with the water turned on for 5 minutes each time. A vichy shower might be on for a total of 15 minutes each hour on very busy days.
  • For hydrotherapy tubs, pedicure spas, etc… what is the water capacity and how often will it be filled in an hour?
  • Total your answers (1-3) to find your peak need. This figure will be the amount of mixed hot water that your particular spa will require at any given time.

There are two approaches (plus combinations of the two) to ensuring that enough hot water is always available. One is to use a water heater(s) with a fast recovery rate to keep up with the demand (recovery time is the time it takes the hot water heater to heat more water to the desired temperature). The other is to provide a thermal storage tank(s) in order to have enough reserved hot water for the peak usage times.

Some Tips:
  • For most day spa applications, a coil type water heater for the fastest recovery time and for their durability seem the most popular.
  • Do not attempt to “get-by” on a residential water heater. A commercial water heating system will be far more effective and durable.
  • “The hotter your water the less you need”. Roughly, to attain F104° water from a F140° supply requires a hot to cold mix ratio of 2 to 1, from F180° supply the ratio is 1 to 1.
  • The capacity of your hot water heating system needs to be able to produce enough hot water for sustained peak usage times.
  • When in doubt get the bigger and faster system. It’s better to over estimate than to try and just get by. Also, it almost invariably costs more to add on later than to plan for future needs in the beginning.

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