Digital mixing valves (DMVs) are rapidly becoming essential components in engineered hot water recirculating systems due to their ability to maintain precise temperature control under dynamic operating conditions. To support this growing application, ASSE 1118, Digital Mixing Valves (DMV) for Hot Water Recirculating Systems, is in its final stages of development as a new American National Standard with an anticipated release in early 2026. See the article “ASSE 1118: Criteria for Digital Mixing Valves” by Terry Burger for the foundational basis of this standard.
ASSE 1118 establishes comprehensive requirements for DMVs installed within recirculation loops where tight temperature regulation is critical for system efficiency and safety. The standard outlines performance criteria, material and physical specifications, testing protocols, and marking requirements specific to these valves.
Unlike traditional temperature control devices, such as those covered under ASSE 1017, the testing procedures for ASSE 1118 are designed to simulate the complexities of a closed-loop system with fluctuating demand. The test setup includes a recirculating rig equipped with a heater to vary temperature input, replicating real-world conditions where temperature demand changes continuously.
To ensure valve reliability and consistency, ASSE 1118 introduces several rigorous testing methods. Across all tests, the passing criterion is a temperature variation of less than 2°F.
One such test, the Outlet Flow Change Test, verifies that the valve maintains temperature stability when flow is reduced from full flow at 10 psi differential pressure to 50% of full flow, simulating extremes in system flow variation.
Another test, the Hot Water Supply Temperature Change Test, evaluates valve performance when the inlet supply temperature fluctuates, assessing how the system responds to temperature shifts caused by changing demand.
Additionally, the Hot Water Approach Test measures temperature creep, defined as the gradual rise in hot water temperature during periods of low or no demand.
By addressing the unique challenges of hot water recirculating systems, ASSE 1118 provides engineers, specifiers, and manufacturers with a robust framework for product design, testing, and integration, setting a new benchmark for precision and performance in digital temperature control.
If you wish to have your product certified with ASSE International, please contact us at listingcoordinator@asse-plumbing.org. To purchase a copy of ASSE 1017 or 1118 — when published — please visit the ASSE International Webstore at www.assewebstore.com.
For questions regarding these standards, contact Christopher White, ASSE Senior Manager of Product Certification, at chris@asse-plumbing.org.
