The Benefits of Right-Sizing Plumbing in Homes & Apartment Buildings

Effective July 1, 2024, the Appendix M, Peak Water Demand Calculator (WDC) will become part of the California Plumbing Code. Instead of using flow rates and flush volumes from the 1940s, the WDC will allow you to “right-size” the cold and hot water distribution systems in homes and apartment buildings using modern information about flow rates and simultaneous use. Does this sound like a snoozer? Actually, it is an environmentally responsible solution that can save energy, time, money, and water.

The presentation will:

  • Share the results of the study used to support the petition for the adoption proceeding
  • Provide an overview of how to use Appendix M in single-family and multi-family projects
  • Provide case studies that show how using the WDC can save $500-$1,000 per apartment in first costs
  • Identify and enable connection with members of the Passive House community who want to learn how to use the WDC in their upcoming projects

Presenter: Gary Klein of Gary Klein and Associates (, and Christoph Lohr (