In the ever-evolving landscape of plumbing technology, precision and performance are no longer optional; they’re essential. As engineered hot water systems grow more sophisticated, the tools and standards that govern them must keep pace. Thus, the need for rigorous performance criteria tailored to the unique demands of recirculation loops.
WHAT IS ASSE 1118?
ASSE 1118, titled Digital Mixing Valves (DMV) for Hot Water Recirculating Systems, is a new American National Standard that is in its final stages of development and expected to be released in early 2026. This standard will supersede ASSE/IAPMO IGC 384, which previously addressed the same category of devices.
ASSE 1118 defines performance, material, physical characteristics, testing protocols, and marking requirements for digital mixing valves used specifically in hot water recirculation loops. These valves are designed to mix hot and cold water to deliver a consistent and accurate mixed water temperature throughout hot water distribution systems.
Importantly, ASSE 1118 does not apply to point-of-use temperature control or emergency fixtures such as eyewash stations and safety showers.
WHY A NEW STANDARD WAS NEEDED
Digital mixing valves are increasingly specified in engineered recirculating water systems due to their ability to maintain precise temperature control. However, until now, there has been no dedicated product standard for DMVs used in this specific application.
Historically, ASSE 1017, Temperature Actuated Mixing Valves for Hot Water Distribution Systems, has been used to specify these devices, but it does not fully address the unique requirements of recirculating systems. From an engineering perspective, mixing valves used in traditional distribution systems and those used in recirculating loops should be considered distinct categories, each requiring its own performance criteria.
Recognizing this gap, ASSE initiated the development of ASSE/IAPMO IGC 384 in 2020 as an interim solution. That document laid the groundwork for ASSE 1118, which now formalizes and expands upon those requirements as a full ANSI standard. The result is a standard that reflects the real-world conditions and performance expectations of modern engineered systems.
KEY DIFFERENCES: ASSE 1017 VS. ASSE 1118
Often referred to informally as “1017 plus,” ASSE 1118 differs from ASSE 1017 in both application and performance expectations. ASSE 1017 covers mechanical and electronic mixing valves typically installed at the source of a hot water distribution system to regulate master temperature (i.e., Master Mixing Valve). In contrast, ASSE 1118 addresses valves installed as part of the recirculation loop, where tighter temperature control is essential for system efficiency. These tighter tolerances — achievable through electronic control — are critical for maintaining consistent temperatures throughout the loop. As such, ASSE 1118 introduces testing protocols that simulate the specific conditions encountered in recirculating systems. See the article “Digital Mixing Valve Test Methods” by my colleague Chris White for details.
HOW DIGITAL MIXING VALVES WORK
Devices covered under ASSE 1118 consist of a hot water inlet, a cold water inlet, a mixed water outlet, a thermostatic sensor, and an electronic mechanism for adjusting the mixed water temperature. The sensor continuously monitors the outlet temperature and adjusts the ratio of hot and cold water prior to mixing to maintain the desired temperature. The standard specifies a control tolerance of ±2 °F, reflecting the precision required in recirculating applications.
REAL-WORLD BENEFITS OF ASSE 1118
The development of ASSE 1118 marks an advancement in plumbing standards and reflects the industry’s commitment to evolving technologies and performance expectations. By establishing clear and specific requirements for digital mixing valves in recirculating systems, ASSE 1118 provides engineers, specifiers, and manufacturers with a reliable framework for product design and system integration.
LOOKING AHEAD: STANDARDS FOR A SMARTER FUTURE
As engineered systems evolve to demand greater precision, efficiency, and reliability, standards must also advance to reflect these changing requirements. ASSE 1118 was developed specifically to address the unique performance characteristics of digital mixing valves in recirculating hot water systems — an area previously underserved by existing standards. The addition of ASSE 1118 to ASSE’s portfolio of standards demonstrates ASSE’s proactive approach to ensuring safety, consistency, and technological alignment with the needs of the plumbing industry.
