The Dangers of Hot Water

Every year, thousands of people in the U.S.A. suffer serious thermal shock
or scalding injuries in their bathtubs, sinks and showers. Additional untold
numbers become ill due to water-borne bacteria, such as Legionella.

Problem: Thermal Shock
Often, injuries in the shower are caused by slips and falls in reaction to a
sudden increase or decrease in water temperature. Ideally, if the supply of
cold or hot water is lost, the water flow should be shut down immediately.
Termination of flow would eliminate the instinctive but dangerous reaction
to move quickly away from a too hot or too cold water stream.

Solution:
Watts Thermostatic Mixing Valves maintain and limit mixed hot water to a
desired, selectable temperature, helping to minimize thermal shock.

Problem: Scalding

More than 90% of scalding incidents occur in the home. The tender skin of very young children and the slow reaction time of the elderly and the handicapped make them most vulnerable to serious hot water burns.Scalding injuries are tremendously painful, and the effects can last for years. Scalding occurs for a variety of reasons. In some cases, water heater thermostats are faulty, or set too high. In others, temperature regulating valves at the domestic hot water source are either malfunctioning or missing altogether. Water heaters are normally set to temperatures above 131°F (55°C) to prevent development of harmful bacteria, such as Legionella, in the water supply. Water at temperatures above 106°F (41°C) are painful. At a temperature of 131°F (55°C), a child can be scalded in less than 4 seconds.

Solution:
Watts Thermostatic Mixing Valves maintain and limit the mixed hot water to a desirable selectable temperature, helping to prevent scalding injury.

Problem: Legionella Bacteria
Legionella is the bacteria responsible for Legionnaire’s Disease, an acute bacterial infection of the lower respiratory tract. This bacterium was first identified in 1977 by the Centers for Disease Control as the cause of an outbreak of pneumonia that caused 34 deaths at a 1976 American Legion Convention in Philadelphia. Pontiac Fever is a less severe, non-pneumonia, flu-like disease that is associated with and likely caused by Legionella bacteria. Legionella is a fairly common water bacteria and has been found to exist widely in many surface water sources such as; lakes, rivers, streams and ponds. It can also be found in ground water sources and some soils. At the levels found in these naturally occurring sources it typically does not pose a threat to public health. When the bacterium enters a domestic water system
it can find an ideal host environment of warm water temperatures (105-115°F), stagnant water areas (storage tanks and dead-end piping legs) and ample food sources (sediment, scale, deposits and biofilm). Under these conditions Legionella can rapidly colonize, forming higher concentrations that can pose the public health threat of Legionnaire’s Disease. There are many methods of controlling colonization of Legionella bacteria. However, a widely accepted and preferred method is to maintain the hot water system storage temperature continually at or above 140°F. Unfortunately, the elevated temperature necessary to minimize the growth of and kill Legionella bacteria has the potential to cause serious thermal shock and scalding injuries.

Solution:
Watts Thermostatic Mixing Valves maintain and limit the mixed hot water to a desirable, selectable temperature allowing for the storage of domestic hot water at the higher temperatures necessary to reduce the risk of Legionella growth in the system.

The Limitations of Pressure Balanced Mixing Valves

Many shower and combination tub/shower mixing valves in today’s homes use a pressure balanced design. Unfortunately, pressure balanced type valves do not automatically control outlet temperatures, nor do they automatically limit outlet temperatures should the supply temperatures dramatically increase or decrease. Such limitations are potentially dangerous. Further, to prevent users from adjusting the valve beyond a safe operating temperature, pressure balanced valves require setting of the limit stop by the installer. In addition, to accommodate future changes in the hot or cold water temperature, the limit stop would need to be re-set. By contrast, Watts Thermostatic Mixing Valves offer precise control of the outlet temperatures, no matter how the supply temperatures or pressures vary over time.

Watts Makes It Safe…

Since 1874 Watts has set the standard for the latest valve technology. Whether it is our pressure reducing valves to regulate steam or water, relief valves to ensure safe operation of water heaters or boilers or backflow prevention devices to help prevent cross-contamination of water supplies, Watts has earned a reputation for safety, reliability and innovation.

A Word about American Society of Sanitary Engineering (ASSE) Standards 1016, 1017 and 1070

Why They Are Used

Supply Systems

Mixing valves provide the following benefits:

1. The water temperature that is discharged directly from a water heater can vary ±10°F or more. This can be due to tolerance of control devices, inlet water temperature changes and stacking (higher water temperatures at the top of the water heater). Use of a thermostatic mixing valve assures constant outlet water temperature even with variations in hot or cold water supply temperature.**
   
2. If a water heater is operated at lower temperatures, high flow demand situations can result in a reduction of hot water supply temperatures if the recovery time of the water heater is not sufficient for the flow demand. Using a hot water extender or mixing valve allows the water heater to be operated at higher temperatures, extending the effective system flow rate and preventing the growth of Legionella.
   
3. To be able to supply peak demands for domestic hot water it is often necessary to provide high capacity water heaters with high recovery rates. Use of a hot water extender can reduce the size/BTU requirements needed to provide capacity for peak system demands.

At the Fixture

Heat loss in the system piping can result in varying temperatures of the hot and cold water supplied to fixtures. The use of thermostatic mixing valves assures constant safe hot water temperature at the point of delivery to the fixture.

** Please refer to specification for the selected model to determine the allowable inlet temperature range to maintain a desired outlet temperature.

Design Considerations

Heat Traps

• All mixing valves used at the source of supply should be trapped. Trapping the valve helps reduce mineral deposits and premature component wear.
  
• Heat traps help reduce convection loss also know as thermosiphoning, increasing system efficiency.

Stop Valves

• All mixing valves should be installed with a means to isolate the valve for service and repair.

Check Valves

• Check valves assure flow of water in one direction. They prevent thermal siphoning of hot water to the cold water supply.
  
• The addition of check valves should be considered whenever the potential exists for extreme differential pressures between the hot and cold water supply.
  
• Check valves are a requirement for compliance with ASSE Standard 1017 applications. Watts Series USG, MMV and 1170 come standard with integral check valves.

Strainers

• Water supply systems should be thoroughly flushed prior to placing mixing valves in service.
  
• Installation of additional strainers in the supply piping is recommended in systems where water can contain particles that could impede the proper operation of the mixing valve. Watts Series MMV and 1170 include inlet filters to provide protection against supply line debris.

Maximum Pressure
This is the maximum pressure that the valve could be subjected to during normal operation. Normal residential water system pressures should be limited to 80psi (552 kPa) as required by national codes.

Maximum Temperature
This is the maximum temperature that the valve could be subjected to during normal operation. Exceeding the maximum temperature could cause failure of internal components.

Minimum Flow
A minimum flow of water through the valve is required to provide accurate temperature control. Water flow below the listed minimum could result in increased outlet deviations.

Minimum Inlet Differential
This is the minimum difference between the hot and cold temperature that is required to produce the desired outlet temperature.

Cautions

At the Fixture

Delivery of water to fixtures intended for use in bathing or washing should always be controlled by valves listed to ASSE Standard 1016 Type T or ASSE Standard 1070 such as Watts Series MMV, L111 and USG mixing valves. ASSE 1016 listed valves provide the user with both scald protection and thermal shock protection. ASSE 1070 listed valves provide the user with scald protection only. These valves should never be set to exceed a maximum temperature of 120°F (49°C). (Watts recommends the maximum temperature of 110°F (43°C) for shower and bathing fixtures.)

Supply Systems

The control of water temperature for the source of supply should be
controlled by mixing valves such as ASSE 1017 listed Watts Series 1170,
L1170 and MMV. These valves can also be used for re-circulation systems to maintain domestic hot water supply temperatures at levels (temperatures above 131°F (55°C)) that prevent the growth of harmful bacteria such as Legionella.

Radiant Heat Systems

Either a Watts 1170 or an L1170 mixing valve can be used for radiant heat systems. However, it is important that a boiler’s high temperature limits do not exceed the maximum temperature rating of the system components. This will protect against component temperature failure should dirt, sediment or other mechanical failure cause a mixing valve to become inoperable.

Periodic Inspection
Regular inspection of mixing valves is recommended to assure maximum valve life and a properly functioning system. Corrosive water conditions, unauthorized adjustments or repairs can be detected during inspection and service of the valve. The frequency of cleaning depends upon local water conditions.