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With 43 years of personal experience in the plumbing industry, I’ve spent decades on litigation cases involving scald burn injuries. I’ve read numerous depositions of property owners and maintenance personnel in charge of plumbing (domestic hot water) systems. Yet there continues to be a widespread misconception that the thermostat dial on a storage-type water heater accurately controls the temperature of the hot water flowing from plumbing fixtures.
In 1973, the American Society of Sanitary Engineering (ASSE) began development of a standard for shower valves addressing the sudden temperature changes associated with pressure imbalances in plumbing systems with two-handle shower valves.
The ASSE 1016 standard was developed in the interests of consumer safety. Several people sent in accounts of disturbing experiences with shower valves that were potentially hazardous, allowing sudden surges of high temperature water to flow from the showerhead. These accounts prompted the initiation of the standard, which was finally ready for publication with ANSI approval in 1979.
Documents and field experiences relating to the behavioral characteristics of different classes of devices (pressure-balancing vs. thermostatic) were studied and evaluated. From this, the standard text was developed. Since that time, extensive research has been conducted toward the development and evolution of the standard in its current form.
The shower control valves covered by the ASSE 1016 standard in 1979 were only those which would, in cases of reduction or loss of cold-water supply, protect the bather.
Use of cold or hot water while showering with an old-style, two-handled shower valve could cause thermal shock and potential scalding from a sudden change in temperature associated with a disturbance in pressure. The new shower valves were pressure-balancing, thermostatic or combination pressure-balancing and thermostatic that open to cold water flowing first; as the valve was rotated open, more hot water was added to increase the mixed water temperature.
The ASSE 1016-compliant valves were required to have rotational “limit-stops,” which would allow the building owner to limit the valves rotation toward the full hot position, and thereby manually be adjusted to limit the maximum temperature setpoint to any desired temperature at or below 120 F. That temperature was chosen after the code and standard committees evaluated the Moritz & Henriques burn studies and decided that a person should have enough time to get out of harm’s way before a serious irreversible burn injury occurs.
The limit-stop is an integral component of combination bathtub-shower valves, and it was designed to allow limiting the maximum hot water temperature to any desirable maximum temperature. Maximum temperature limit-stops were unheard of then, and they are still not very well-known today.
According to discussions I had with Norm Kummerlan, the former ASSE 1016 committee chairman, soon after the bathtub/shower valve manufacturers started adding the limit-stop feature to comply with the new ASSE 1016 standard, many of the manufacturers started shipping the shower valves with the limit-stop adjusted to fully restrict or limit the hot water in the mixed flow leaving the bathtub/shower valves.
This resulted in a flood of complaints by consumers and plumbers who were unaware of the adjustable limit-stop feature and thought the bathtub/shower valves were defective because they did not allow the water to get hot flowing from the bathtub or shower fixture fitting. Many valves were removed.
Manufacturers chose to take the easy route rather than continue with the flood of troubleshooting calls and provide training on the limit-stop feature. Instead, they chose to ship the bathtub/shower valves in the wide-open position and include instructions on how to set the limit-stop with a manual adjustment (both initially and seasonally to account for changes in incoming cold water) to limit the temperature of the hot water flowing from faucets.
Today, the codes clearly restrict the temperature flowing from a fixture. Almost everyone knows that the maximum hot water temperature flowing from a bathtub/shower fixture fitting should be no greater than 120 F; they just don’t understand how it should be accomplished. Many people rely instead on the water heater thermostat for temperature control in the hot water system and at the fixtures.
Voluntary Standards and the CPSC
More than 40 years ago, the development of products and product standards for bathtub-shower valves limiting the maximum temperature of hot water flowing from fixture fittings was overseen by the Consumer Product Safety Commission (CPSC). It was regarded as the solution to an ever-increasing number of scalds burn injuries and thermal shock (slip and fall injuries).
This rendered an ongoing debate over what the thermostat on water heaters should be set to when they were manufactured to prevent scalding hot water from being produced, with the hope that “a well-publicized program will encourage retrofitting of existing installations with these new devices.”
In 1978, Kenneth W. Feldman, a Seattle-area doctor, with the support of several signatories, sent a letter to the recently formed CPSC and requested that the CPSC “require that water heaters be fabricated with a maximum thermostat setting of 130 F.” Feldman later explained his choice of 130 F to the CPSC in another letter; he said he originally “suggested limits of 120-125 degrees F on the factory preset temperature;” however, as a “concession,” he “was willing to increase the limit to 130 F” to allow for adequate dishwashing.
However, he did question whether water at 130 F was necessary to sanitize dishes. Feldman pointed to an earlier study commissioned by the CPSC, known as the A.D. Little study, and to his own investigation and research for the proposition that 130 F is really only necessary to prevent spotting on the dishes: “I find a scarred face or arm on a child much more cosmetically unacceptable.”
The CPSC received the letter on June 30, 1978. On the advice of the Office of General Counsel (OGC), the CPSC treated the letter as a “petition under section 10 of the CPSA [Consumer Product Safety Act, 15 U.S.C. sections 2051-2089 (1972)], requesting the issuance of a consumer product safety rule for new gas or electric residential water heaters to require such heaters to include a maximum thermostat setting of [130 F] and to require the heaters display warning labels describing the hazards of hot water and instructions for setting water heater temperatures.”
By statute, the CPSC had a “120-day period for granting or denying” the petition, which period began to run from the date the letter was received.
Even before Feldman’s 1978 letter, the CPSC was leaning toward voluntary standards. In a letter dated Sept. 7, 1976, the CPSC, through William V. White, director of bureau of information and education, wrote: “Present thinking at the [c]ommission seems to favor a voluntary rather than a mandatory standard for bathtub and shower areas.” After receiving Feldman’s letter, the CPSC vocalized its position that voluntary standards were the preferred method to address scalding hazards.
In a draft of a July 1978 letter to U.S. Sen. Warren Magnuson of Washington, the CPSC wrote that it worked with the bathtub and shower industry, as well as manufacturers of components, in the development of safety requirements for water temperature-limiting devices, stating that these requirements were incorporated into a voluntary standard being developed by ASTM Committee F-15 on Consumer Product Safety.
Many in the industry knew ASSE was developing the ASSE 1016 standard at the time, but they did not mention it by name other than to say they favored the voluntary standards route. The CPSC wrote: “If these standards are [adopted] by the industry, and the products are installed in the domestic water systems, they will significantly reduce the hazards of scald burns in bathtubs and shower stalls for newly constructed homes. Hopefully, a well-publicized program will encourage retrofitting of existing installations with these new [devices].”
Simultaneously with the course of the petition, the CPSC directed its staff to work with the industry to develop voluntary standards. At its March 15, 1979, meeting, the commission encouraged the gas and electric water heater industries to continue their “ongoing efforts to develop voluntary safety standards[.]” In its denial of the petition, published in the Federal Register on Feb. 9, 1981, the CPSC wrote: “The [c]ommission has decided to deny this petition, in part, because of the voluntary efforts to lower factory pre-set temperatures on water heaters and to provide cautionary labeling addressing the scald hazard.”
For a period of time thereafter, CPSC staff continued to monitor standards development by attendance at various meetings.
I do not have access to the version of the statute as it existed in 1978; however, the current version of the statute requires the CPSC to defer to voluntary consumer product safety standards rather than promulgate a consumer product safety standard. Only if voluntary standards would not “eliminate or adequately reduce the risk of injury” and where it is unlikely there “will be substantial compliance with such voluntary standards” can the CPSC issue a mandatory consumer safety rule.
When the CPSC does promulgate a consumer product safety standard, the standard shall consist of either, or both, requirements in terms of performance requirements or requirements in terms of warnings and instructions.
As a result of the activities surrounding the “Seattle City Light Petition,” as Feldman’s letter was known as, water heater manufacturers began shipping their water heaters with their thermostats “pre-set” to 120 F. However, the idea of a pre-set thermostat is misleading because, for some thermostat models, the dial must be rotated to a “pilot-lighting” setting to light the water heater, and then turned to a “desired” setting. In other words, even if pre-set, the dial must be moved.
Despite the CPSC’s belief that existing hazardous installations would soon be retrofitted with the new devices, in development, building owners and other interested parties lobbied against mandating replacement of existing shower valves with code-compliant shower valves, despite the fact that not replacing the two-handled valves left the existing plumbing system unsafe.
In 2013, a study approved by the Johns Hopkins Institutional Review Board (https://bit.ly/3dVxfRR) was conducted to report on the hot water temperatures in urban homes: “Although water heater manufacturers adopted a voluntary standard in the 1980s to pre-set thermostats on new water heaters to [120 F], tap water scald burns cause an estimated 1,500 hospital admissions and 100 deaths per year in the United States.”
The study concluded: “Our results suggest that hot water temperatures remain dangerously high for a substantial proportion of urban homes despite the adoption of voluntary standards to pre-set temperature settings by manufacturers. This research highlights the need for improved prevention strategies such as installing thermostatic mixing valves to ensure a safer temperature.”
Using the Query Builder feature (https://bit.ly/2Uzv1Ry) of the National Electronic Injury Surveillance System (NEISS), which is a statistically valid injury surveillance system operated by the CPSC, the national estimate of the number of persons (all ages) with injuries (all types) associated with water heaters (all types) for the years 2015-2019 is 24,509.
As a volunteer firefighter for 34 years, I am familiar with the database maintained by the National Fire Incident Reporting System, which is what fire and EMS departments used to record the mechanism of injury after an incident; fire departments are usually the first responders to a medical emergency, and more than 80 percent of their calls are medical.
If a “911” call is made regarding a medical emergency, the fire department is dispatched first. An ambulance service, if operated independently of the fire department, is dispatched second. The data collected, and code assigned to the data, is slightly variable depending on the person inputting the data and the level of notetaking or detail in incident reports, including whether the person inputting the data was present at the scene.
Therefore, using the Query Builder feature of the NEISS, I performed a few other queries for a given time period, varying only the injury category and associated product category, as follows:
• Injury-type limited to scald burns: 1,653
• Injury-type limited to scald burns and associated product expanded to water heaters (all types), piping (all types) and bathtub and shower structures: 3,986
• Injury-type expanded to scald burns and thermal burns and associated product expanded to water heaters (all types), piping (all types) and bathtub and shower structures: 26,724
Point-Of-Use Temperature-Limiting Controls
As a result of Feldman’s letter and the CPSC response, many people still erroneously believe a storage-type water heater can accurately control the outlet temperature. Recent efforts by ASSE to develop new standards intended for tankless heaters with controls to shut-off the energy in order to limit the temperatures produced a category of water heaters with a temperature control within the same range as mixing valves.
This prompted many attempts to change the codes and eliminate the long-standing language in the codes prohibiting the water heater thermostat from being used to control the hot water temperature at fixtures. That language needed to stay for the storage-type water heaters, but it is now gone.
As a design professional or a contractor or a plumbing inspector, it is important to realize that there still needs to be point-of-use temperature-limiting controls to balance the pressure and prevent thermal shock and scalding or provide thermostatic protection without further mixing downstream.
Storage-type water heaters allow the temperature to rise approximately 20 degrees from the bottom of the heater to the top because of thermal layering and stacking in a storage tank. In addition, the gas-fired water heaters with combination gas control valves allow the temperature to rise another 10 degrees, making it possible for a storage-type water heater to have temperatures leaving the water heater up to 30 degrees higher than the thermostat setpoint.
So, using the thermostat on a water heater to set a temperature of 120 F and then experiencing a normal condition in a household — short, intermittent uses of hot water to rinse dishes or your hands while cooking or baking — the water heater cycles each time the hot water is drawn from the heater and a small amount of cold water is drawn into the bottom of the water heater. The burner comes on to heat up the cold water in the bottom of the water heater, causing the already hot water at the top to be overheated. With a water heater set to 120 F, it can have 150 F hot water leave the water heater.
• At 120 F, it takes about 4.8 minutes for an adult to receive a second-degree blistering burn; it takes about 1.2 minutes for a child to receive a second-degree blistering burn.
• At 150 F, it takes about 0.9 seconds for an adult to receive a second-degree blistering burn; it takes about 0.2 seconds for a child to receive a second-degree blistering burn.
In larger buildings, the temperature drop across the building makes it nearly impossible to have accurate temperature control at all fixtures. The possibility of a 30-degree rise and the heat loss across the building distribution piping system is why the water heater thermostat knob should never be considered as an acceptable control for safe hot water temperatures at fixtures.