Scalding hot water from fixture faucets and fittings accounts for more than 25 percent of all scald burns in children. The elderly and the physically impaired also are at increased risk of scald burns because they have thinner skin and slower reactions. They often cannot recognize a hazard and get out of harm’s way before a serious burn can occur.
Control of scalding and Legionella bacteria
I have always said, “Scald burns and Legionella bacteria growth in hot water systems, which can lead to Legionnaires’ disease, are 100 percent preventable.”
Scalding and Legionella bacteria can be controlled when domestic hot water systems are designed, installed and maintained to keep hot water storage and distribution temperatures above the maximum Legionella growth temperature of 122 F.
Appropriate temperature controls must be used at or near fixtures to reduce the maximum hot water delivery temperature from fixtures to 120 F or below.
Single-handle shower controls to control scalding
and thermal shock
The attempt to prevent scalding and thermal shock injuries which often lead to slip and fall injuries was the driving force that brought about the invention of temperature control devices. In 1924, a plumbing manufacturer developed the first shower valve with a pressure-compensating element to address thermal shock common in two-handled shower valves.
Shower faucets before then typically had two-handled faucets that allowed the water from the hot and cold-water system to be mixed in a mixing chamber. A two-handled faucet or shower valve would have sudden changes in temperature as other fixtures were used in the plumbing system, which caused pressure disturbances that, in turn, caused sudden changes in temperature — either hot or cold.
The two-handled design provided the opportunity for a bather to receive serious scald injuries if someone accidentally turned off the cold water first while bathing or showering, which would leave only the hot water flowing to the shower. The original design had a pressure-balancing piston to adjust for thermal shock.
Adjustable limit-stops on shower valves
A couple of decades after the introduction of the pressure-balancing shower valve, newer designs of the valves entered the market. Other manufacturers developed additional safety components for shower valves, which included a maximum temperature limit-stop adjustment.
The limit stop adjustment allowed a single-handle valve to be manufactured and installed with a field-adjustable maximum temperature setting to a temperature at or below 120 F. The single-handle opened to the cold-water flow first and, as the handle was rotated farther, the valve added more hot water.
Hot water is often stored at or around 140 F, which was, and still is, the basis for water heater storage temperatures in many manufacturers’ equipment sizing calculations.
In uncirculated hot water tanks, the stored hot water temperatures could rise significantly above 140 F due to thermal layering (heat rising to the top of an uncirculated water heater).
Another phenomenon that causes the hot water temperatures to rise significantly above the water heater thermostat set-point is stacking. It occurs when there are multiple, intermittent, short draws of hot water from a water heater, causing cold water to enter the bottom of the hot water tank. The thermostatic element senses the cold water and turns on the burner, even when the water at the top of the water heater is well above the thermostat setting.
ASSE Temperature Control Device Standards
Each device covered by an ASSE product performance standard has specific applications as to where it is intended to be used. The authority having jurisdiction (AHJ) has the final approval of all installations but one must be aware of the code requirements and the application must allow the device for that application.
In addition, the installation must comply with the scope listed in the product standard. The installation also should comply with the manufacturer’s installation requirements, which may be more restrictive than the code adopted by the local jurisdiction.
The ASSE Product Performance Standards for these devices are: ASSE 1016/ASME A112.1016-2011/CSA B125.16-11, Performance Requirements for Automatic Compensating Valves for Individual Showers and Tub/Shower Combinations; ASSE 1017, Performance Requirements for Temperature Actuated Mixing Valves for Hot Water Distribution Systems; ASSE 1062, Performance Requirements for Temperature Actuated Flow Reduction (TAFR) Valves for Individual Fixture Fittings; ASSE 1066, Performance Requirements for Individual Pressure Balancing In-Line Valves for Individual Fixture Fittings; ASSE 1069, Performance Requirements for Automatic Temperature Control Mixing Valves; ASSE 1070/ASME A112.1070-2015/CSA B125.70-15, Performance Requirements for Water Temperature Limiting Devices; ASSE 1071, Performance Requirements for Temperature Actuated Mixing Valves for Plumbed Emergency Equipment; ASSE 1082, Water Heaters with Integral Temperature Controls for Distribution Systems. (Currently finalized, awaiting board approval as of this writing.); ASSE 1084, Water Heaters with Integral Temperature Controls for Point-of-Use Applications. (Currently finalized, awaiting board approval as of this writing.); ASSE 1085, Water Heaters with Integral Temperature Controls for Use with Emergency Fixtures. (Currently under development as of this writing.)
ASSE recommends that design professionals, plumbers, owners, installers, maintenance personnel, specifiers, inspectors, engineers, educators, trainers and code officials use caution when determining which device is correct for a particular application or installation.
In some applications, installing the wrong device or installing the device in the wrong location can lead to potentially serious scalding situations, thus exposing the end user to potentially scalding hot water temperatures. Furthermore, installing the wrong device can lead to a false sense of security by the ultimate user. Therefore, it is extremely important to make sure installation of the proper device is in the proper location. It must be maintained in accordance with the manufacturer’s installation and maintenance instructions.
Description of Temperature Control
Shower and Tub/Shower Combination Valves (ASSE 1016). Shower valves that comply with ASSE 1016 are automatic temperature and/or pressure-compensating valves intended to be installed at an individual shower or tub/shower combination fixture.
The model plumbing codes require all shower and tub/shower fixtures to have temperature controls that comply with ASSE 1016-2011/ASME A112.1016-2011/CSA B125.16-11, Performance Requirements for Automatic Compensating Valves for Individual Showers and Tub/Shower Combinations.
The user has access to the ASSE 1016 flow and final temperature controls. No further mixing should occur downstream of the ASSE 1016 device.
These devices are intended to control the water temperature to wall-mounted or ceiling-mounted hand-held showers; showerheads; body sprays, either in the individual shower or tub/shower combination fittings; and tub spouts, when part of tub/shower combination fittings.
There are three different types of shower valves meeting this standard: pressure-balancing, thermostatic (mechanical and electronic) and combination pressure balancing and thermostatic.
The showerhead flow rate must not be less than the manufacturer’s published minimum flow rate for the valve (device). The temperature limit stop must be set at the time of installation and may need to be periodically adjusted for variations in water temperatures. These devices provide both scald and thermal shock protection.
Hot Water Distribution Systems (ASSE 1017)
Temperature-actuated mixing valves for hot water distribution systems are used for controlling in-line water temperatures in domestic hot water systems to a relatively uniform temperature.
These valves should comply with ASSE 1017, Performance Requirements for Temperature Actuated Mixing Valves for Hot Water Distribution Systems or a comparable CSA standard listed in the code. When used, installation of these devices should be at or near the outlet of the hot water source only.
These valves are designed to provide a relatively uniform water temperature to the hot water distribution system, which makes setting maximum temperature limit stops in the system more reliable than a system without a mixing valve where uncirculated water heater discharge temperatures can vary by more than 30 F greater, or 15 degrees less, than the water heater thermostat set-point.
ASSE temperature-actuated mixing valves allow the water to be stored and distributed at higher, more stable temperatures, extending the amount of hot water available and also reducing the chance of Legionella bacteria growth in the tank and distribution piping. (See ASHRAE 188 and ASHRAE Guideline 12.)
These valves are not intended for point-of-use applications because of the large temperature variation. Valves must be sized to match the flow requirements of the system and not sized based on the pipe size (see Table 1). 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.
To prohibit the cross-flow of hot or cold water through the valve, supplementary check valves should be installed for devices that do not include integral check valves by the manufacturer.
Individual Supply Fittings — TAFR Valves
Temperature-actuated, flow reduction (TAFR) valves, when used, should be installed on the discharge outlet of the fixture fitting or integrated into fixture fittings.
These valves must comply with ASSE 1062-2006, Performance Requirements for Temperature Actuated Flow Reduction (TAFR) Valves for Individual Fixture Fittings.
They are intended for use in-line with, or integrated into, individual plumbing supply fittings such as showerheads, bathtubs, whirlpool bathtubs, utility sink faucets, kitchen sinks and lavatory faucets.
They are designed to automatically reduce flow down to a trickle within five seconds of outlet temperatures greater than a preset actuation temperature not to exceed 120 F (48.9 C). During the five-second response period, the bather may be exposed to temperatures more than the setpoint of the device.
After actuation, the device is required to have a trickle flow, which allows the temperature controls on the faucet to be adjusted to a lower temperature to reset and open the device automatically at a predetermined lower temperature, or with the use of a manual reset mechanism.
These devices can be used on existing fixtures such as the showerhead associated with an older-style two-handle, nonpressure or temperature-compensating shower valve to provide scald protection. Typically, a TAFR device is used in an existing installation where no other form of scald protection is provided.
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. These devices provide an additional level of scald protection only and do not provide thermal shock protection.
Caution: These valves automatically reduce discharge flow to a trickle if water temperature exceeds a preset limit. This trickle can be as much as 0.25 gallons per minute (0.95 L/m). When this device is installed on a bathtub spout and the outlet temperature exceeds the preset limit, and if the bathtub drain is closed, the bathtub could fill with extremely hot water from this allowable trickle.
Caution: Some ultra-low-flow showerheads may still have a full spray pattern when the flow through this TAFR device is reduced.
In-Line Pressure-Balancing Devices for Individual Fixtures (ASSE 1066)
Automatic pressure-balancing in-line valves are used to equalize incoming hot and cold-water line pressures. This minimizes mixed water temperature variations due to pressure fluctuations when used in conjunction with a mixing valve or two-handle valve set.
These valves must comply with ASSE 1066, Performance Requirements for Individual Pressure Balancing In-Line Valves for Individual Fixture Fittings. They are not designed to limit the maximum outlet temperature at the point-of-use. These devices provide thermal shock protection for pressure disturbances only and do not provide scald protection if the incoming hot or cold-water temperature changes.
Thermostatic Temperature-Limiting Devices with Downstream Mixing Permitted (ASSE 1070)
Water temperature-limiting devices are intended to limit the hot or tempered water temperature supplied to fittings for fixtures such as sinks, lavatories, bidets or bathtubs to reduce the risk of scalding.
These devices must comply with ASSE 1070-2015/ASME A112.1070-2015/CSA B125.70-15, Performance Requirements for Water Temperature Limiting Devices. They are intended to supply hot or tempered water to plumbing fixture fittings or be integral with plumbing fixture fittings supplying hot or tempered water.
These devices shall have fixed (nonadjustable) temperature setting; or temperature setting that can be adjusted and locked in position; or adjusted with the use of a tool to protect against adjustment by the user; or further mixing downstream is allowed.
These devices have an integral water temperature-limiting capability. The user control allows the outlet temperature to be adjusted up to a maximum temperature of 120 F (49 C). They provide scald protection only and do not provide thermal shock protection.
Mixing Valves for Plumbed Emergency Equipment (ASSE 1071)
Temperature-actuated mixing valves are intended to be used as a component to provide tepid water for emergency eye wash, eye wash/shower, drench showers and combination units that comply with the requirements of ANSI Z358.1.
These valves must comply with ASSE 1071-2012, Performance Requirements for Temperature Actuated Mixing Valves for Plumbed Emergency Equipment. These valves, by themselves, do not meet the requirements of ANSI Z358.1.
They consist of a hot water inlet, a cold-water inlet, a mixed water outlet, a temperature controlling element and a means for adjusting the mixed water outlet temperature while in service. These valves also have the means to limit the maximum outlet temperature under normal operating conditions.
Provisions shall be made so that the temperature cannot be inadvertently adjusted. These valves shall include a means of preventing cross-flow. Ideally, these devices are intended to be installed as close as possible to the plumbed emergency equipment. These valves provide scald protection only and do not provide thermal shock protection. They provide cold water bypass flow in the event of hot water failure.
Note: ASSE 1071 devices should be installed at individual fixtures. Emergency plumbed equipment must be flushed frequently, per industry standards, or per the water management or water safety plan to minimize stagnant water.