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The American Society of Sanitary Engineering’s (ASSE) 1070 Standard, Performance Requirements for Water Temperature Limiting Devices, first published in 2004, is an industry standard for a point-of-use or in-line temperature-actuated mixing valve with a maximum temperature limit feature. The device is one that restricts or limits the maximum temperature of the hot water supplying a fixture/fitting(s). It can be used as a final tempering device, or there can be further tempering with the addition of cold water downstream of the device.
Originally, the standard provided for both an adjustable and maximum limit feature. As I discuss further below, the adjustable feature has all been written out of the standard.
Prior to the development and publication of the ASSE 1070 standard, the industry used whatever it could use to mix hot and cold water to provide tempered water to handwashing sinks, shampoo bowls, bathtubs, whirlpool bathtubs, bidets, shampoo sinks, pedicure bowls, a group of lavatories or other fixtures requiring tempered water.
Mechanical mixing tees, shower valves and other mechanical mixing valves were used to mix hot and cold water for these applications, but these devices were neither temperature-actuated nor thermostatic mixing valves. These devices were simply proportional mixing tees and shower valves, the latter of which was most often the pressure-balanced type, listed to the ASSE 1016 standard, and not the thermostatic type.
Some contractors would install a mechanical mixing tee made up of a tee with two ball valves to mix the flow of hot and cold water. However, this arrangement could not accurately sense or control the outlet temperature. In addition, it had no check valve to prevent crossover flow, which is an extremely dangerous condition from a pressure disturbance and scalding standpoint.
Other contractors would install a shower valve under a fixture (and, thus, hidden from the user) and use the shower control as an in-line control valve to temper the hot water to a group of lavatories, bathtubs, whirlpool bathtubs, bidets, shampoo sinks and similar fixtures. To account for this “new” use of shower valves, the title of the ASSE 1016 standard was changed so as to broaden its perceived scope for the use of the valve for “individual fixtures” instead of only for “individual showers.”
This allowed the continued misapplication of shower valves until the ASSE 1070 standard came along; the ASSE 1016 standard’s title was changed back to address individual showers and tub-shower combinations.
The use of nontemperature-compensating mixing valves in these applications was a cause of concern for many industry professionals. The concern was that if a mechanical mixer or nonthermostatic (pressure-balancing) device was installed, it would not react to significant changes in incoming cold or hot water temperatures; thus, there would be no scald protection provided by these installations under certain conditions.
The use of ASSE 1016 shower valves to temper water for these other fixtures was not fit for the purpose. That standard was developed to specifically address two things: thermal shock and scalding. Thermal shock is addressed by either a pressure-balancing or thermostatic component within the mixing valve device that quickly responds to pressure or temperature changes associated with pressure disturbances in the system.
Scalding is addressed by the rotational limit-stop feature, which prevents the valve from being rotated to a dangerously hot temperature. Further, the ASSE 1016 standard was developed for showers and tub-showers with a flow rate matching that of a showerhead (2.5 gallons/minute). Where other flow rates are involved, there is no guarantee of temperature control accuracy.
In lower-flow fixtures, temperature control within the limits of the ASSE 1016 standard cannot be maintained. And, for supplying a group of lavatories, the flow rate far exceeded a 2.5 gpm flow rate.
ASSE 1070 Origins
During the late 1990s and into the early 2000s, there was industry debate regarding the need for a new standard to address products for these point-of-use or in-line tempering applications with a maximum temperature limit feature for nonshower fixtures requiring tempered water. This prompted the new ASSE 1070 standard for temperature-limiting valves. The scope of the ASSE 1070 standard was:
“These devices are intended to supply tempered water to plumbing fixture fittings, or be integral with plumbing fixture fittings supplying tempered water. The device shall be equipped with an adjustable and lockable means to limit the setting of the device towards the hot position. Where the device is integral to the fixture fitting, it shall comply with the requirements of ASME A112.18.1.
“1.2.2 Flow Range
“The manufacturer shall designate the minimum and maximum flow rate and pressure drop of devices other than those designed into fixture fittings. The flow rates for devices designed into fixture fittings shall be in accordance with ASME A112.18.1.
“1.2.3 Working Pressure
“The device shall be designed to function at a maximum working pressure of not less than 125.0 psi (861.8 kPa).
“1.2.4 Temperature Range
“The device shall be designed with an adjustable outlet temperature that shall include the range 105.0 F to 110.0 F (40.6 C to 43.3 C). The device shall operate with inlet cold water temperatures 39.0 F to 80.0 F (3.9 C to 26.7 C) and with inlet hot water temperatures 120.0 F to 180.0 F (48.9 C to 82.2 C).
“1.2.5 Cross Flow
“The device shall include a means of preventing cross flow when tested in accordance with Section 3.7.”
Pat Higgins, the former author of this code column, was a licensed master plumber and consultant on plumbing, codes, standards, product approval and regulatory approval to numerous industry companies and trade organizations. He was one of the leading advocates for thermostatic mixing valves for bathtubs, whirlpool bathtubs and similar applications.
Before the ASSE 1070 standard was completed, Pat proposed a code change calling for thermostatic valves on bathtubs and whirlpool bathtubs; unfortunately, he passed away in 2001 before the code hearings took place. During those hearings, when the committee called for the proponent of the proposed code change to speak, I stood up and spoke on Pat’s behalf in support of his proposal.
I am uncertain what became of that first proposal, but code sections calling for thermostatic temperature-limiting devices for water discharged from public lavatories, bathtubs, whirlpool bathtubs, bidets and, later on, shampoo bowls and pedicure basins eventually made it into both model codes.
In 2003, the Uniform Plumbing Code added new sections limiting water temperature in public lavatories and bathtubs. However, they did not state what device to use, but they did prohibit the water heater thermostat from being used because code officials were aware that the water heater thermostat does not accurately control hot water distribution temperature:
“414.1 Limitation of Hot Water Temperature for Public Lavatories. Hot water delivered from public use lavatories shall be limited to a maximum temperature of 120 F. The water heater thermostat shall not be considered a control for meeting this provision.”
“421.0 Limitation of Hot Water in Bathtubs. The maximum hot water temperature discharging from the bathtub filler shall be 120 F.”
In 2006, the International Plumbing Code added new sections limiting water temperature in bidets, public lavatories and bathtubs, requiring the use of an ASSE 1070 device:
“408.3 Bidet water temperature. The discharge water temperature from a bidet fitting shall be limited to a maximum temperature of 110 F (43 C) by a water temperature-limiting device conforming to ASSE 1070.”
“416.5 Tempered water for public hand-washing facilities. Tempered water shall be delivered from public hand-washing facilities through an approved water temperature limiting device that conforms to ASSE 1070.”
“424.5 Bathtub and whirlpool bathtub valves. The hot water supplied to bathtubs and whirlpool bathtubs shall be limited to a maximum temperature of 120 F (49 C) by a water temperature limiting device that conforms to ASSE 1070, except where such protection is otherwise provided by a combination tub/shower valve in accordance with Section 424.3.”
A sentence was added to the end of section 424.3 to emphasize that devices conforming to the new ASSE 1070 standard could not deal with thermal shock if a mixing valve was downstream.
“424.3 Individual shower valves. Individual shower and tub-shower combination valves shall be balanced-pressure, thermostatic or combination balanced-pressure/thermostatic valves that conform to the requirements of ASSE 1016 or CSA B125 and shall be installed at the point of use. Shower and tub-shower combination valves required by this section shall be equipped with a means to limit the maximum setting of the valve to
120 F (49 C), which shall be field adjusted in accordance with the manufacturer's instructions. In-line thermostatic valves shall not be used for compliance with this
section. [Emphasis added.]”
The ASSE 1070 standard is ideal for those nonshower applications requiring tempered water. It was quickly adopted by the model codes, which now require the use of an in-line ASSE 1070 mixing valve in the hot water supply to various specified fixtures. Because these devices include an adjustable maximum temperature-limit stop and a tamper-resistant feature, it is possible for the model codes to prescribe different maximum temperature limits for the various specified fixtures.
ASSE 1070 was promoted as a standard to solve point-of-use temperature control issues over a wide range of flows. The industry debated about maximum temperatures; scald prevention was the main concern. The intent was to have an adjustable mixing valve with a temperature-limiting feature to adjust the maximum outlet temperature.
Specific discussion centered on using these devices on single-pipe tempered water to metering faucets used on groups of lavatories over a wide flow range; however, some states have unnecessarily mandated one mixing valve per fixture. (Note: ASSE 1069 is a separate standard for temperature-actuated mixing valves for gang showers, where there is a single-temperature water supply with metering buttons. These are commonly used in schools, gyms, detention facilities and similar applications.)
A few years later, in 2015, a newly formed harmonization working group consisting of members of ASSE, the American Society of Mechanical Engineers, and the Canadian Standards Association chose to lower the maximum allowable temperature from the ASSE 1070 temperature-limiting device. However, one organization arguably did not have a standard covering a product for this application, and the other had a thermostatic mixing valve standard, but not for these applications.
The harmonizing effort had a lot of people unfamiliar with the history of the ASSE 1070 standard and its applications. The harmonization committee added requirements and changes for the device to shut down at lower temperatures, so adjustability is no longer an option; the device shuts down after the temperature gets moderately warm.
I have always said that ASSE 1070 devices should not include a factory-fixed temperature at which they shut down (or are limited to) because it is design-restrictive and does not address many conditions in the field.
For example, if a maximum temperature of 110 F is required, then some areas of the country in the northern climate may not be able to get a hot bath in a cast-iron tub. Filling a cast-iron tub requires a slightly higher fill temperature because the heat will be drawn out of the water by the cold cast iron. If the tub filler is limited to 110 F or lower, the bather will likely not get a warm or hot bath. But if the standard allows 120 F and an adjustable-limit stop to a lower temperature, it could allow a warm bath around 105 F to 110 F in colder climates during the winter.
I have always promoted the ASSE 1070 device as having an adjustable maximum temperature-limit stop and maximum temperature setpoint with tamper-resistant features. Recent reductions in the maximum allowable temperature for the device make it useless in some applications.
With a higher adjustable maximum temperature, it allows an owner or a designated maintenance person to set the device to a maximum of whatever the local code or the application calls for, such as 120 F, or lower to 115 F or 110 F or 105 F. With an adjustable device, the mixed water flowing from the fixture outlet can be checked and adjusted by the owner or maintenance person seasonally for changes in incoming cold-water temperatures, and any time there is a change in the hot water distribution temperature.
Where there are multiple fixtures requiring different maximum temperatures, the product needs an adjustable maximum temperature based on its application.
I’m hoping the standard will be revised soon to address the original intent of the device.
An ASSE 1070 valve works by tempering the hot side of the valve to limit the maximum outlet temperature when mixed with cold water. Other tempering or limiting devices may be downstream of the 1070 device; the temperature is adjustable, and can be used for single or multiple fixtures.
Additionally, the standard requires the 1070 device to maintain +/- 7 F, which is not as stringent as for a 1016 shower valve (+/- 3.6 F) due to the perception that the application is less critical (showering versus handwashing or bathing) when tested at the manufacturers stated minimum flow. The revisions to the 1070 standard provide that a device will be rejected if at any time during the temperature variation test the outlet temperature exceeds 120 F.
Before harmonization, the ASSE 1070 standard required thermostatic mixing protection; if the incoming water temperature changed, there would be constant protection. And if the valve failed in setting the temperature, water flowing through the valve would close to a trickle. After harmonization, the thermostatic requirement was removed from the standard.