With the world’s heightened focus on infection control, local municipalities, the Centers for Disease Control and Prevention, the U.S. Occupational Safety and Health Administration and other plumbing authorities are calling for buildings to use several methods to reduce the development of waterborne pathogens. One of the foremost measures recommended by the CDC and OSHA is maintaining higher domestic hot water temperatures throughout your facility.
The idea is simple. The higher the temperature, the better the infection control.
While COVID-19 isn’t waterborne, Legionella and other waterborne pathogens and bacteria that can wreak serious havoc on a facility and its occupants are on the rise. An October 2020 article in the Smithsonian Magazine notes that in 2018 (the most recent data collected), the CDC reported the highest number of Legionella cases ever in the United States (http://bit.ly/3cxUNMG).
Maintaining higher temperatures across a building’s plumbing system will improve infection control in the domestic water system and reduce the potential for Legionella development. Yet this practice is in direct opposition to the industry push for energy-efficient design over the last decade that led many engineers and building owners to revamp their approach to plumbing infrastructure and lower building-wide distribution and circulation temps.
If the industry is to transition to higher hot water supply and return temperatures, plumbing engineers will need to shift from central temperature control applications to point-of-use control. This allows a building operator to maintain higher temperature circulation and reduce the temperature at the point of use.
Establishing a New Building Temperature Set-Point
The CDC (http://bit.ly/2YF6SaJ) and OSHA (http://bit.ly/3oEDuMj) are calling for buildings to circulate temperature across their plumbing infrastructure at a minimum of 122 F to 124 F. This is about 10 to 15 degrees higher than most facilities are currently operating.
Making this change is a lot more complicated than raising the circulating water temperature by 10 degrees.
For one, water will need to be introduced into the plumbing loop at a minimum of 125 F in a smaller building and possibly up to 135 F in larger buildings to circulate and return water regularly at 124 F or above. These higher source-distribution temperatures are needed to account for normal temperature drops within the piping system.
Higher distribution and return water temperatures building-wide also mean engineers and building operators must focus on scald prevention. Even a 10-degree increase in water temperature can have a serious effect on scalding at a faucet. As a general rule of thumb, it takes 10 seconds to get a serious scald from 135 F and only three seconds at 140 F.
Prevent Scalding with Proper Valve Specification
Scald prevention can be attacked by specifying the right valves for your temperature set-points across a facility. From faucets to showers to emergency fixtures, valve specification will be the magic bullet necessary to increasing building water temperatures while ensuring occupant safety.
The American Society for Sanitary Engineering (ASSE) is the industry authority on developing performance standards, testing and certification of valves for the use of scald prevention. ASSE set seven standards for different valve types based on location and use in a plumbing system (https://bit.ly/39GnFk3).
Many of the ASSE certifications should be common language in a plumbing engineer and building owner’s repertoire. We will discuss the most commonly used standards, the applications for each standard and the tricks to success for each.
One key factor to this article is the understanding of what is “scalding.” ASSE defines scalding as: “Hot water exposure for a time period long enough to cause a thermal injury. Scald burn injuries can increase in severity at higher hot water temperatures or with longer exposures to a given hot water temperature.”
This is notably different than another phenomenon in plumbing systems known as “thermal shock,” which ASSE defines as “a significant sudden change in temperature from hot to cold or cold to hot, or hot to hotter that causes a bather to violently react, which can lead to a slip and fall injury.”
It is important to understand the difference. ASSE developed performance criteria for both, but not all ASSE standards discussed protect against both scalding and thermal shock
Individual Shower and Combination Tub/Showers: The ASSE 1016 Valve
ASSE 1016 automatic temperature-compensating and automatic pressure-compensating valves can come in three varieties: valves that adjust outlet temperature only, cold and hot water pressure, and some that do both.
Automatic pressure-compensating valves, commonly known as pressure-balancing shower valves, compensate for fluctuating cold and hot water pressures at the inlet to maintain a constant outlet temperature. They protect against the thermal shock of hot water when a nearby toilet is flushed, which drops the cold water supply pressure to the shower valve.
Pressure-balancing valves are less costly and work great under the assumption that the temperatures will not change with the valve's use. With that said, they are essentially “blind” to the incoming cold and hot water temperatures, so any change in water temp at constant pressure will affect the outlet temperature of the valve
Automatic temperature-compensating valves, commonly known as thermostatic shower valves, adjust the mixing ratio of cold and hot water to provide a constant outlet temperature. They will compensate for changes in water temp at constant pressure; however, they will not protect against thermal shock due to varying system pressures.
When distribution temperatures were lower for energy conservation measures, it was common to use a master mixing valve to determine the system operating temperature. At the showering fixture, pressure-balancing valves were common for thermal shock protection due to inevitable pressure fluctuations in a plumbing system.
However, with rising distribution temps, pressure-balancing valves will likely be replaced by thermostatic valves that are not blind to the higher temps and offer better scald protection.
Best practices for the use of these valves are:
• The showerhead flow rate must not be less than the manufacturer’s published minimum flow rate for the valve (device).
• The temperature limit stop in a pressure-balancing valve must be set at the time of installation. It may need to be periodically adjusted for variations in water temperatures, such as seasonal cold water changes. In a typical building with operations set at 120 F, shower valves could be set at 115 F.
In response to the new CDC rule, if the building operators modify the system distribution set-point to provide minimum circulation at 124 F, the shower valves will experience temps higher than the 115 F set-point and need to be reset.
Distribution Systems: The ASSE 1017 Valve
As mentioned previously, ASSE 1017 mixing valves have traditionally been used throughout plumbing distribution systems at the hot water source to control system temperatures. Now that higher temperatures are being implemented across distribution systems, there is potentially less of a need for ASSE 1017 valves. Overall, plumbing engineers will need to specify valves at the point of use with higher distribution temperature requirements.
However, these valves will not become extinct. ASSE 1017 valves can still ensure a uniform distribution temperature, even if it is higher than in the past. They also allow engineers to store water at high temperatures while distributing at a lower but still a “high” temperature. They can assist in reducing Legionella; however, engineers and owners must weigh the cost of an ASSE 1017 valve over the value it provides.
A strong player in this market is the digital master mixing valve, which provides ASSE 1017 protection along with digital readout and data logging of inlet and outlet temperatures. It can be set to provide alarms upon failure and performance out of a specified tolerance. Many owners see the value in this information and system safety.
Whether a mechanical or digital ASSE valve is used, the same considerations are still present:
• These valves are not intended for point of use applications.
• Valves must be sized to match the following flow requirements of the system:
Flow Rate (gallons/minute)
Allowable Temperature Fluctuation
More than 40 gpm
• Further mixing downstream is allowed to provide final temperature control to protect against scalding.
• These devices used alone do not provide thermal shock protection or adequate scald protection.
TAFR Valves: The ASSE 1062 Valve
Although not commonly used, a temperature-actuated, flow-reduction (TAFR) valve can be applied to a fixture outlet to reduce flow to a trickle within five seconds, in the event the outlet temperature exceeds a preset value, not to exceed 120 F. During the five-second response period, the bather may be exposed to temperatures in excess of the set-point of the device.
Important to note is that these devices provide scald protection only; they do not provide thermal shock protection. TAFR valves are not intended to be installed in place of devices complying with ASSE 1016, ASSE 1017, ASSE 1066, ASSE 1069 or ASSE 1070.
The ‘Nonshower’ Pressure-Balancing Valve: The ASSE 1066 Valve
Another uncommonly used valve, the ASSE 1066 automatic pressure-balancing valve, can be applied like an ASSE 1016 valve for sinks, lavatories, etc.
The 1066 is blind to incoming water temperatures and only provides thermal shock protection, not scald protection. Since most codes require an ASSE 1070 valve used for handwashing, they do not have a very common application.
Gang Shower Valves: The ASSE 1069 Valve
For applications in locker room or penal showers, where individual shower valves are not used for safety and or anti-ligature applications, an ASSE 1069 valve can be used and connected directly to fixture outlets.
The valve will determine the final temperature of everything connected downstream, and the end-user typically doesn’t have access to the valve for temperature adjustment. The valves do, however, provide thermal shock and scald protection.
Sink Faucets: The ASSE 1070 valve
Water at handwashing applications should not surpass 110 F. Design engineers can use a mixing valve at the point of use to make this happen. The trick is specifying the right one.
For sink, lavatory, bidet or bathtub applications, ASSE recommends using the ASSE 1070 valve. These devices are intended to supply tempered water to plumbing fixture fittings or be integrated with plumbing fixture fittings providing tempered water. This valve's successful performance depends on key factors such as a minimum flow rate and associated pressure drop. Additionally, a temperature deviation is required for the ASSE 1070 valve to work optimally.
Here’s what’s necessary:
• Cold and hot water temperatures must come in at 10 to 15 degrees from the valve outlet set-point. For example, to maintain the 110 F water, the hot water at the valve must be a minimum of 125 F and cold water a maximum of 95 F.
• The ASSE rating allows for a deviation of the set-point, plus or minus 5 or 6 degrees.
Most importantly, pair the performance characteristic with the value of the application. If LEED certification is a priority and the facility is outfitted with low-flow fixtures, it’s critical to know which valves to select should your facility be increasing the hot water temperature throughout the piping system. Raising your system’s hot water temperature without considering mixing valves at regular faucets will put occupants at
Emergency Fixtures: The ASSE 1071 Valve
Emergency eyewash, eye/face wash and shower applications typically operate at 85 F and work off an ASSE 1071 valve. The person engaging an emergency fixture will typically need to use it for 15 minutes. Thermostatic valves employed in emergency fixtures are paying attention to the incoming hot and cold water.
Should the thermostatic valve fail, it is typically programmed to bypass the system and release only cold water. Cold water is better than no water when there’s acid on the skin or poisonous liquid in the eye. When raising your building’s temperature set-point, make sure the ASSE 1071 is configured correctly to reduce scalding incidence.
The need for strong infection control in every type of facility isn’t going to go away any time soon. Rather, this trend is likely to continue and become even more prominent through the end of the COVID-19 pandemic and beyond.
In preparation for this new long-term focus, plumbing designers and engineers will need to examine their existing infrastructure and, when considering new facilities, plan for infection control and higher temperature water flow. This will require a real departure from the updated set-points, equipment and fixture specification we’ve been trained to design to in the last decade, when sustainability and energy efficiency took center stage.
While the future of building plumbing systems is unknown, a few trends are likely to take us into the next decade of design:
• Higher-temperature waters are here to stay. The push to reduce exposure to Legionella and other waterborne pathogens will only increase and serve as a major push behind the design and circulation of plumbing systems. The future may demand even hotter water temperatures and increased flow simultaneously.
• We’re going to see a shift away from low-flow fixtures. Design engineers are now concluding that low-flow fixtures aren’t the best option for plumbing infrastructure on a facility-wide level. While it’s easy to build a low-flow faucet, it’s not easy to make a mixing valve prevent scalding at a low-flow rate.
Maintaining and tracking the flow rate will help building engineers continually adjust the temperatures to keep occupants safe and reduce the potential spread of bacteria such as Legionella.
With the call to raise building water temperature, plumbing engineers have a new-found purpose. Minimizing the risk of waterborne pathogens in buildings and, more importantly, preventing building occupants' scalding will take our engineering know-how and creative solutions designed to meet all the simultaneous needs of our facilities. This will be the next frontier in plumbing expertise.