Master Mixing Valve Field Study

California Plumbing and Energy Codes do not mandate master mixing valves (MMV) for domestic hot water (DHW) recirculation systems, though they are commonly used in multifamily and elder care facilities. Research has shown that adding digital master mixing valves (DMMV) can reduce water heating energy use by 6.5% to 18% for multifamily buildings with heat pump systems.  This study evaluated the energy impacts of DMMV in five sites, including a restaurant, multifamily building, senior facility, clinic, and hotel, comparing performance with and without MMV. The research found an average energy savings of 4.5%, with results varying from 11.4% to -4.9%. While gas-fired systems showed savings, heat pump water heaters (HPWH) did not perform as expected due to set point sensitivity. DMMV offers energy savings potential, but successful integration requires proper contractor training and quality control during installation. Non-energy benefits, like pathogen control and reduced runouts, further support DMMV use.