Domestic Hot Water Electrification Strategies

Electrifying your domestic hot water (DHW) system is a straightforward and cost-effective building decarbonization strategy. Electric DHW equipment is widely available, relatively inexpensive, and commonly used, plus, these systems are generally easy to install and replace, smoothing the transition from natural gas to electricity.

How to Evaluate DHW Systems

Prior to electrifying your DHW, evaluate existing fixtures and hot water demand to minimize the hot water load and ensure the building is operating efficiently. Although electricity typically has a higher cost per British thermal unit (Btu) than natural gas, careful system sizing and proper insulation of the equipment and the building envelope can help manage utility costs.

Implement Water Conservation Strategies

Target performance improvements in buildings with significant DHW demands, such as residence halls, gymnasiums, and kitchens. Evaluate the potential to reduce water use in these buildings at hot water fixtures (such as sinks/faucets and showers) by upgrading all fixtures to low-flow options, which can be performed during the building’s renovation cycle or at end-of-life. Reducing the overall potable hot-water demand reduces the energy required to heat that water.

Evaluate Existing Domestic Hot Water Infrastructure

Evaluate the conditions and interconnectivity of the existing DHW system, from the water supply to the heating equipment to the end-use fixtures. This can include:

• Confirming that all pipes and tanks are well-insulated, particularly in cold climates
• Ensuring there are no leaks in the system
• Evaluating the domestic hot water heater to determine the current efficiency and whether maintenance could be improved

Compare Electric DHW Systems

There are several electric domestic hot water systems on the market:

Heat pump water heaters (HPWHs) offer high efficiency but are less suited for instantaneous heating due to lower temperature lift. They use electricity to transfer heat from the air or ground to heat water rather than converting electricity directly to heat. This reduces energy consumption by up to 60% compared to an electric resistance water heater. Pairing HPWHs with solar thermal systems can further reduce energy use by harnessing renewable energy to preheat water, thus lowering the demand on the heat pump system.

Electric resistance water heaters work by converting electricity directly into heat and, while less efficient than HPWHs, still offer a relatively low-cost, low-maintenance solution, especially in colder climates.

Hybrid water heaters combine heat pump and electric resistance technologies in a single unit. They provide efficient operation with built-in backup during periods of extreme cold or high demand, making them ideal for space-constrained, high-occupancy settings like residence halls. Operating these systems during off-peak hours can further reduce energy costs.

Tankless systems eliminate standby losses and are well-suited for applications with intermittent or peak demand that require quick hot water delivery, such as residence halls.

Explore Waste Heat Harvesting Opportunities

Consider recovering and using waste heat from existing campus processes (e.g., heat rejected from cooling systems, kitchen facilities, data centers, and sewage systems) to generate hot water. This heat recovery could be achieved through heat exchangers that use waste heat to support domestic hot water production.

Integrate With Renewable Energy Systems

Consider integrating domestic hot water with available renewable energy systems. Solar thermal collectors or other renewable energy systems can provide hot water for domestic use or power electric equipment such as heat pump water heaters.

Planning and Next Steps

Electrifying DHW systems is an essential step toward decarbonization. By transitioning to heat pump water heaters, electric resistance or tankless water heaters, and higher-efficiency kitchens, campuses can significantly reduce their carbon footprint.

To maximize success beyond electrification, campuses should explore integration with other systems such as energy storage, renewable energy, and waste heat recovery. The future planning and phasing for improving those systems will determine whether integration with the DHW system is an option. An integrated approach can help reduce the potential utility cost increases associated with electrification and help to share and balance demand between different types of thermal and electrical loads.

Consider if a retrofit should take place campus-wide, at individual buildings in a phased approach, or for specific use categories. For example, renovations for restrooms and shower rooms can commonly include separate upgrades in a standalone pathway from other campus improvements, which also supports the consolidation of multiple orders for bathroom equipment.

Resources

• Storage Strategies
• Renewable Energy Strategies
• U.S. Department of Energy Better Buildings Solutions Center: Decarbonizing the Commercial Kitchen