Improve Energy Efficiency of Hot Water Distribution Systems in Multifamily Buildings

Eliminating crossover in water piping could save energy and water

Enovative Group, Inc.


Venice, CA

Recipient Location


Senate District


Assembly District



Amount Spent



Project Status

Project Result

The research found multiple ways to detect crossover, verified detection methods, andassessed the practicality of using a method in the field. The research team applied thesedetection methods on approximately 100 multifamily buildings, and results show thatcrossover may be in as many as 52% of the multifamily buildings. Recommendations include:install check valves before shower valves or on risers feeding shower valves; install isolationvalves around shower valves; require pressure balance, thermostatic, or combinationpressure balance/thermostatic shower valves with an integral check stops. Cross-over was considered for the 2022 Title 24 standards but not incorporated.

The Issue

When cold water crosses over to the hot water lines, this phenomena is called "crossover" and results in unbalanced distribution systems and energy and water waste due to the rapid cool down of hot water in the pipes. This problem is most prevalent in multifamily buildings. Research is needed to determine the extent of the problem and energy loss and identification and testing of possible solutions to prevent crossover at the fixtures.

Project Innovation

This research project quantified the energy and water impacts of crossover and unbalanced recirculation loops in domestic hot water systems associated with multifamily buildings and identified best practices and tools for identifying and pinpointing these issues. Crossover occurs when hot water goes into the cold water line, and vice versa. Preventing, identifying and repairing crossover issues can reduce energy, water and other waste (less wasted water going down the drain) in central hot water systems.[br /]
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Project Benefits

The research found multiple ways to detect crossover, verified detection methods, and assessed the practicality of using a method in the field. A sample of approximately one hundred multifamily buildings in California were tested, and results show that crossover may be in as many as 52% of the multifamily buildings. After monitoring and fixing the crossover problem in 10 buildings, the natural gas savings was approximately 16%. The research identifies opportunities for future building efficiency codes and standard changes to prevent crossover in multifamily buildings.

Consumer Appeal

Consumer Appeal

Identifying and correcting crossover results in greater customer/tenant satisfaction since they will receive hot water sooner.

Lower Costs


Research results estimate 16% gas savings and up to 30% water savings due to elimination of cross-over. This will result in benefits to multifamily residents receiving hot water sooner at the fixture, and landlords and occupants can benefit by lower costs.

Environmental & Public Health

Environmental Sustainability

Significant natural gas savings will reduce greenhouse gas emissions. Water savings will eliminate water waste. Water savings of 30% can be very beneficial in communities that are facing water shortages and may not have a reliable water source.

Key Project Members

Project Member

Gabriel Ayala

Project Manager

Match Partners


Enovative Group, Inc.


Contact the Team