A temperature control valve that meets ASSE1066. (Photo courtesy of Watts Industries.)

Boilers and water heaters produce hot water and their performance requirements are covered by various national standards. These hot water-producing systems are for the production of hot water but not the final control of the hot water as it is used in plumbing systems. The control of the hot water after it leaves its source must be accomplished by additional control devices.

There are generally two control issues with the hot water systems. The first is high-limit temperature control, and the second is pressure control. The danger when high temperatures are not controlled is scalding, and the danger when pressure is not controlled is a rapid change in mixed water temperature at outlets such as showers that can cause thermal shock. Scalding often results in third-degree burns and scarring. Thermal shock often results in injuries from slips and falls as the bather tries to move away from a sudden temperature change.

The areas of concern in plumbing systems are the delivery points of hot water to tubs, showers, sinks and numerous other fixtures in commercial and institutional settings. The concerns are for both newly designed systems and retrofitting existing systems. With the variety of designs that are possible for hot water systems, there needs to be a variety of plumbing devices to provide the necessary hot water control.

The American Society of Sanitary Engineering (ASSE) is the standards writing organization that has published the performance standards for these hot water control devices. It all began over 30 years ago with the development and publication in 1973 of ASSE Standard 1016, first titled, "Individual Shower Control Valves Anti-scald Type." It was the first of this type of product performance standard for the plumbing industry. A full understanding of the ASSE series of temperature control standards is required for the system designer to provide the proper degree of scald and/or thermal shock protection in a system. ASSE is the ANSI-accredited standards developer in the United States for these types of safety devices. All of the published ASSE standards for devices that control hot water are referenced in all the model plumbing codes. ASSE is in the process of developing several additional product standards to afford even more design flexibility in plumbing systems while still providing the necessary hot water control.

Starting chronologically, the family of hot water control standards is as follows:

ASSE 1016, 1996 edition, "Individual Thermostatic, Pressure Balancing, and Combination Pressure Balancing and Thermostatic Control Valves for Individual Fixture Fittings." This standard covers three classes of products that compensate for either incoming temperature fluctuations, incoming pressure fluctuations or both. These devices are installed at the point of use and are permitted to serve only one fixture fitting. These devices are required to be set at the time of installation to a maximum outlet temperature of 120

A central thermostatic mixing valve that meets ASSE 1017. (Photo courtesy of Leonard Valve Co.)

ASSE 1017, 2002 edition, "Performance Requirements for Temperature Actuated Mixing Valves for Water Distribution Systems." Commonly known as a master mixing valve, this device is installed at the source of the hot water, i.e. the boiler, and controls the hot water within a set range by blending the hot water with cold water in response to the thermostatic element. The minimum outlet temperature range the device can be set at is 105

Temperature control devices that meet ASSE 1062. (Photo courtesy of Cash Acme.)

ASSE 1066, 1997 edition, "Performance Requirements for Individual Pressure Balancing In-line Valves for Individual Fixture Fittings." This device does not limit the maximum outlet temperature. Its function is to balance the hot and cold water pressure to a fixture fitting, thereby stabilizing the outlet temperature once it has been set by the fixture fitting. This is a secondary device to a temperature control device.

A thermostatic mixing valve that meets ASSE 1017. (Photo courtesy of Bradley Corp.)

ASSE 1069, 2004 Draft Standard, "Performance Requirements for Automatic Temperature Control Mixing Valves." These devices control the water temperature delivered to individual or multiple fixture fittings. These devices will protect against both thermal shock and scalding. These devices will react to fluctuations in both the incoming hot and cold water pressures and the hot and cold water temperatures. They will control the outlet water temperature to within +3

A temperature control valve that meets ASSE 1016-1070. (Photo courtesy of Watts Industries.)

ASSE 1070, 2004 edition, "Performance Requirements for Water Temperature Limiting Devices." These devices control and limit the outlet water temperature to 120

A valve that meets 1016-1070. (Photo courtesy of Watts Industries.)