Maintaining hot water temperatures
Scalding and thermal shock entered the plumbing engineers’ vocabulary more than 35 years ago with the advent of water conservation. Showers always were known to increase in temperature when someone activated a flushometer valve, but the temperature increase was minimal when showerheads were unrestricted, flowing at 8- to 10-gpm rates.
When the showerhead flow rate was lowered to 3 gpm, the spike in hot water temperature from the flushing of a water closet spiked to scalding temperatures. Seeing or feeling, an increase in temperature of 35° to 40° F was not uncommon.
Our response, which was tremendous as an industry, was to protect the user of hot water fixtures with valves that provided a level of safety. Initially, it started with thermostatic mixing valves complying with ASSE 1017. However, we soon realized that these thermostatic mixing valves, while good, did not provide complete safety. To this day, the plumbing codes do not recognize ASSE 1017 valves as the final level of protection against scalding or thermal shock.
The standards that provided an adequate level of safety are ASSE 1016, ASSE 1070, ASSE 1071 and ASSE 1069. The first standard being for shower valves, the next three for thermostatic mixing valves.
It’s been long understood the thermostat on water heaters cannot adequately control the temperature of the hot water. We are so convinced that water heater thermostats are poor controlling devices that we added requirements to the plumbing codes stating you cannot use the water heater thermostat to control the upper limit of the hot water temperature.
Of course, 35 years ago, temperature swings of 30° in a water heater were considered acceptable. Therefore, the water heater thermostat is completely unreliable.
In those 35 years, the industry has gotten much better with the controls on water heaters. Where those aforementioned temperature swings were once the norm, modern water heaters are controlling temperatures of the water to within 3° to 7°. The question becomes: are the plumbing codes out of date?
Time for an upgrade?
The plumbing codes probably do need to be revised, but there is nothing available to prove our modern-day water heaters are safe. This has resulted in the request for new standards to evaluate water heaters for equivalency to the thermostatic mixing valves.
ASSE has taken charge of developing three new standards which have been assigned the numbers: ASSE 1082, ASSE 1084 and ASSE 1085.
The first standard, ASSE 1082, is being developed as equivalent to ASSE 1017. In other words, the water heater will be able to control the outlet temperature to within a narrow range of temperatures, but it will not have any additional safety features.
The first thing many people ask is, “Why develop a water heater for equivalency to a valve that is not allowed in the plumbing code for protection against scalding or thermal shock?”
I will admit this was my first thought when the development of this water heater standard was announced. However, the water heater can be used in buildings where ASSE 1016 or 1070 shower valves are installed at the fixtures. The ASSE 1082 water heater can be used to set the upper temperature limit currently required for all shower valves and bathtub fillers. If the upper temperature is set, the contractor can save considerable time by not having to adjust every shower valve after installation. The water heater would serve that function.
The next standard under development is the ASSE 1085 standard for water heaters for emergency fixtures. The standard will be equivalent to ASSE 1071. These water heaters are unique in that they will only supply tepid water to emergency fixtures. The outlet water temperature can’t rise to above 100° under severe test conditions. The water heater is required to provide a supply of tepid water for a period of 15 minutes, the length of time required to use an emergency fixture. Similar to an ASSE 1071 valve, if the water heater fails, cold water must freely run through the water heater. The last thing you want in an emergency fixture is for the water to turn off as a safety measure. It is better to have cold water than no water for an emergency fixture.
The last standard to be developed is ASSE 1084. This standard will regulate water heaters that are equivalent to ASSE 1070 thermostatic mixing valves. Similar to ASSE 1070 valves, in the event of failure of the hot or cold water, the water heater will shut off the full flow of water. This is a safety measure that will prevent scalding and thermal shock.
One of the difficulties in setting requirements for this type of water heater is the safety feature for shutting off the flow of water. If a water heater gradually runs out of hot water, there is no thermal shock in a shower. We have all experienced a tank-type water heater running out of hot water as our shower temperature lowers to the point of turning off the water. The gradual change in temperature is not a thermal shock hazard. However, the instantaneous loss of hot water can result in thermal shock.
The goal of ASSE is to have these new standards completed by the end of this year. As I write this column, two of the standards are out for ballot with the working groups. Once the ballot achieves consensus, the standard then moves to the Standards Committee and public review. If you would like to receive a public review copy of any one of the standards, be sure to contact ASSE.
If the standards are published by the end of this year, they can then be proposed for inclusion in the IAPMO Uniform Plumbing Code and ICC International Plumbing Code. If successful during the code-change process, the standards will not appear in the plumbing codes until the 2021 editions. It’s something to look forward to in the code.
Prior to that time, you always can consider the use of water heaters complying with these standards, once they are published, on an alternative approval basis. Since these water heaters provide an equivalent level of safety to the existing valve requirements, most code officials will likely approve their use.