The simple act of turning on the shower belies the complex interplay of water temperature and pressure variables behind getting that temperature just right.
A shower is actually a combination of several different plumbing products – including the showerheads and handles that users see, as well as the behind-the-wall piping and the shower valve – that deliver the mix of hot and cold water to each user's optimum comfort.
All shower valves sold in the United States must be “pressure-balancing” or “thermostatic.”
- Pressure-balancing guards against a sudden unanticipated change in shower water temperature caused by the simultaneous usage of other fixtures, such as a toilet or a washing machine, that demands a large quantity of water quickly.
- Thermostatic shower valves maintain comfortable outlet temperatures, even with changes to the inlet water temperature. Some thermostatic valves even adjust the outlet water temperature with inlet pressure changes as well.
The result of rapid temperature changes of the shower water is “thermal shock” that can lead to dangerous falls, caused by trying to scramble away from sudden discomfort. Scalding is also a real risk without pressure-balanced or thermostatic shower valves, where the user is actually burned by the extremely hot water. Pressure-balance and thermostatic valves limit the swing of water temperatures experienced by the user.
Shower heads with lower flow rates tend to make the plumbing system more sensitive to the pressure changes created when other fixtures are operated while the shower is being used. This increased sensitivity can result in increased risk of thermal shock and scalding. The risk of thermal shock and scalding can be further magnified with lower flow replacement shower heads installed in a pre-existing plumbing systems designed to accommodate showerheads with higher flow rates.
To minimize the risk of scalding and thermal shock, plumbing professionals ensure that acceptable methods of controlling hot water temperatures are installed when installing showerheads with less than 2.5 gpm.
In new construction and renovated plumbing systems, that means the shower should be equipped with a valve that complies with ASSE 1016 or ASME A112.18.1/CSA B125.1 and is specifically designed to provide thermal shock and scald protection at the flow rate of the showerhead being used. Ideally, the showerhead/valve combination is verified by the product manufacturer(s).