Introduction to Heat Pump Water Heating with High-Performance Distribution Systems
Water plays a vital role in nearly every building type, supporting a wide range of critical human, mechanical, and operational needs. Among all building types, residential type occupancies tend to be the highest users, especially when it comes to domestic hot water for basic health and hygiene like sanitation, drinking, and food preparation. As heat pump water heaters (HPWHs), become more widely adopted, it’s increasingly important to pair them with high-performance distributions systems to ensure optimal energy efficiency, occupant comfort, and overall system effectiveness.
A typical domestic water heating system consists of three main phases: generation, distribution, and use. The generation phase involves heating the water through a dedicated system, such as HPWHs, conventional water heaters, or centralized boilers. Next, the distribution phase is responsible for delivering the heated water to its point of use through a network of pipes. A high-performance distribution system is designed to minimize energy waste by optimizing key factors such as flow control, insulation, layout efficiency, and pipe sizing. These design choices influence how quickly hot water reaches fixtures and how much heat is lost along the way. The final phase of the process is use, which is when hot water is drawn by appliances or fixtures for daily activities. While water heater efficiency is often a primary focus, the distribution system is frequently overlooked in building design. This oversight can result in poor system performance, including long wait times for hot water and significant energy losses during delivery. These issues could be avoided with thoughtful system planning.
Why Plumbing Design Matters for HPWH Performance
As buildings transition from gas to electric systems like HPWHs, plumbing distribution systems must evolve too. Many designs still rely on outdated sizing methods, like the 1940’s Hunter’s Curve or Uniform Plumbing Code (UPC) tables, originally developed for high-flow fixtures and conventional gas systems. These approaches often lead to oversized piping, increased hot water delivery times, unnecessary heat loss, and high material costs.
To support modern efficiency goals, the 2022 California Plumbing Code introduced Appendix M, which uses the International Association of Plumbing Mechanical Officials’ (IAPMO) Water Demand Calculator. This performance-based method more accurately reflects today’s low-flow fixtures and usage patterns. Appendix M promotes compact layouts, right-sized piping, low-loss systems, and compatibility with demand-controlled recirculation systems. Therefore, helping hot water reach fixtures fast while using less energy and water. This modern approach improves comfort for occupants and ensures that HPWHs can operate at their full potential, making it a critical tool in designing efficient, low-carbon buildings.
Key Components for a High-Performance Distribution System
High-performance plumping systems go beyond just right-sized piping. To truly optimize domestic hot water (DHW) efficiency and comfort, especially in systems using HPWHs, modern technologies like thermostatic balancing valves (TBVs), master mixing valves (MMVs), and variable volume circulating pumps (VVCPs) play a critical role. These smart components improve temperature control, reduce wait times, conserve energy, and maintain safe water delivery. When integrated with HPWHs, they support a more efficient, responsive, and resilient hot water system—especially in high-rise multifamily and other residential buildings.
Essential Design Strategies of High-Performance Distribution Systems
- Minimize pipe length to reduce heat loss and wait time
- Right-size piping using IAMPO’s Water Demand Calculator to balance flow rate and energy efficiency
- Insulate pipes to maintain water temperature
- Streamline plumbing layout to improve performance and reduce material use
- Incorporate MMVs to ensure safe, consistent delivery temperatures and protect against scalding
- Use TBVs to maintain balanced flow in recirculation loops, reduce hot water wait times, and improve overall system efficiency
- Incorporate VVCPs to adjust flow based on real-time demand, reduce pump energy use, and minimize heat loss during low-demand periods
What Are the Benefits?
- Improved energy efficiency
- Faster hot water delivery
- Reduced water waste
- Leads to lower operating costs over time
- Supports decarbonization and sustainability goals
- Enhanced comfort and safety
- Better system control and reliability
What Are the Challenges/Constraints?
- Additional upfront costs or complexity in retrofit projects
- Requires thoughtful design and planning
- May require a more experienced contractor
- Systems with VVCPs, TBVs, and MMVs may need proper setup and calibration to function as intended
- Right-sizing and layout optimization may be limited by architectural or retrofit conditions
Contact us today to enroll and build resiliency into your project.
Resources
- U.S. Environmental Protection Agency. (n.d.). Efficient hot water distribution: A best practices guide for new residential construction. Guide for Efficient Hot Water Delivery Systems pdf – epa.gov
- International Association of Plumbing and Mechanical Officials. (n.d.). Water demand calculator—California edition. WATER DEMAND CALCULATOR CALIFORNIA – Water Efficiency and Sanitation Standard for the Built Environment – iapmo.org
- TRC. (2023, August). 2025 Title 24 CASE report: Multifamily domestic hot water – Final. Multifamily Domestic Hot Water.pdf – title24stakeholders.com
- Northwest Energy Efficiency Alliance. (n.d.). NEEA. Advancing Energy Efficiency in the Northwest. Advancing Energy Efficiency in the Northwest- neea.org
