ICC Commercial Mechanical Practice Exam

What is the minimum temperature that would require a mixing valve to be integrated into a potable water-heating system?

1. 120°F

2. 130°F

3. 140°F

4. 150°F

The correct answer is: 140°F

The integration of a mixing valve in a potable water-heating system is crucial for ensuring safety and comfort in water delivery, especially in residential and commercial settings. The minimum temperature that triggers the requirement for a mixing valve is driven by the need to prevent scalding while maintaining adequate water temperature for various uses. Setting the water heating system to a higher temperature, such as 140°F, is standard practice to reduce the potential growth of harmful bacteria, such as Legionella, in the water heater. However, water at this temperature can cause burns in a matter of seconds if it comes into contact with skin. By incorporating a mixing valve, the system can blend the hot water with cold water to deliver water at a safer temperature, typically around 120°F for point-of-use applications, significantly reducing the risk of scalding. The choice of 140°F as the minimum operational temperature ensures a balance between hygiene and safety. Water heating systems set lower than this temperature might not effectively prevent bacterial growth, while temperatures higher than 140°F can present serious burn risks without proper mixing mechanisms. Thus, a mixing valve becomes essential when the system operates at this minimum threshold.