Showerhead Flow Rates - Safety and Performance Issues
The Plumbing Manufacturers Institute (PMI), the trade association of plumbing product manufacturers, has made the promotion of water efficiency a top priority and has included it in its mission statement (www.pmihome.org). PMI’s members are the industry leaders in producing innovative water efficient plumbing technologies relied upon to meet indoor water conservation goals.
PMI’s commitment to water efficiency includes promoting the development and use of higher efficiency showerheads (showerheads that use less than the 2.5 gallons per minute mandated by Federal law). Higher efficiency showerheads represent a promising opportunity to conserve water.
However, there is a critical need to ensure that water savings are being realized, performance in meeting consumer needs, and health and safety are being maintained with the use of higher efficiency showerheads. To address these needs, PMI and other industry stakeholders are working through a joint effort between the American Society of Mechanical Engineers (ASME) and Canadian Standards Association (CSA) to develop requirements that address acceptable showerhead efficiency without compromising performance or safety. The resultant criteria will help to ensure shower heads perform as intended, and serve as a critical resource for regulators, water providers and fellow efficiency advocates who are developing water efficiency and green building guidelines.
With regard to bather safety, PMI believes it is important for installers and users to understand there is an increased potential for bathing hazards known as thermal shock and scalding with the use of higher efficiency showerheads. The potential risks may be further magnified in existing plumbing systems without the protection of automatic compensating shower valves designed to reduce these risks.
WHAT ARE THERMAL SHOCK AND SCALDING AND WHAT ARE THE CONSEQUENCES?
It is widely understood that exposure to hot water or a sudden unanticipated change in water temperature in the shower can present a hazard. Thermal shock is a sudden and uncomfortable change in water temperature causing an abrupt physical reaction of a person, which could cause a serious injury from a slip or fall. The temperature change can be either toward colder or hotter water. Rapid temperature changes are caused by simultaneous usage of other fixtures, such as a toilet, or an appliance, such as a washing machine, that demands a
large quantity of water, quickly. This creates a temporary pressure imbalance between the hot and/or cold water supply. The imbalance changes the ratio of hot and cold water, which leads to a change in outlet temperature. If the temperature change is great enough, it can also result in scalding.
LOWER FLOW SHOWERHEADS INCREASE THE RISK OF THERMAL SHOCK AND SCALDING
In general, 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 rapid temperature changes of larger magnitude and the 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 preexisting plumbing systems designed to accommodate higher flow rates.
When various states and the federal government were implementing laws to reduce showerhead flow rates to 2.5 gallons per minute in the early 1990’s, PMI led the plumbing industry in updating and implementing product standards and plumbing code requirements to mitigate the risks of temperature-related shower injuries exacerbated by lower flow showerheads. As a result, the vast majority of plumbing codes throughout the United States and Canada now require individual automatic compensating valves complying with either ASSE 1016 or ASME A112.18.1/CSA B125.1 to provide thermal shock and scald protection in the shower. It is important to note that these product standards and plumbing codes assume that an automatic compensating valve is serving a 2.5 gpm showerhead, and do not assure that it is sensitive enough to provide thermal shock and scald protection at lower flow rates.
WHAT SHOULD BE DONE
PMI believes that the most effective way to minimize the risk of scalding and thermal shock is to ensure that acceptable methods of controlling hot water temperatures are installed when installing lower flow rate showerheads (less than 2.5 gpm).
In new construction and renovated plumbing systems, the shower should be equipped with an automatic compensating valve that complies with ASSE 1016 or ASME A112.18.1/CSA B125.1 and specifically designed to provide thermal shock and scald protection at the flow rate of the showerhead being used. Ideally, the performance combination should be verified by the product manufacturer(s).
Existing shower valves without protective features provide no thermal shock or scald protection. As such, the shower valve should be replaced with an automatic compensating shower valve complying with ASSE 1016 or ASME A112.18.1/CSA B125.1 that is specifically designed to provide thermal shock and scald protection at the flow rate of the showerhead being used; or a plumbing professional should evaluate the entire hot water delivery and use system to determine whether additional protective controls are necessary to make the installation safer.
Finally, Regulators, water providers and fellow efficiency advocates should refrain from establishing shower head flow rate and performance requirements outside of the ASME/CSA process. Instead, interested stakeholders are encouraged to participate in this process, and utilize the resultant shower head ASME/CSA criteria as a reference in green building and water efficiency guidelines.