Midwest 120-Volt heat pump water heater field study

Heat pump water heaters (HPWHs) use heat pump technology to heat water more efficiently than standard water heaters, including electric resistance and gas- or propane-fired water heaters.

Typical HPWHs need a 240-volt connection to work, which may require costly electric upgrades. A 120-volt heat pump water heater (120V HPWH), however, plugs into a regular electrical outlet. While these units avoid the need for electric upgrades, they also heat water more slowly—a potential concern for utility programs based in cold climates such as the Midwest.

On behalf of Consumers Energy, ComEd, Xcel Energy, and Focus on Energy, Slipstream conducted a field study to test how well 120V HWPHs work in real Midwest homes.

What we found

Phase I: Market assessment

We assessed the technology potential, barriers, and applications for 120V HPWHs across the Midwest. This included market research and modeling that showed that the technology could provide sufficient hot water for residents with typical household usage.

However, interviews with plumbers, distributors, and retailers indicated that they would be unlikely to sell the product without validation of 120V HPWHs' high performance in cold climates.

Phase II: Field demonstration

In Phase II, the research team recruited 27 single-family Midwestern households to participate in a year-long field study. We installed a 120V HPWH and monitoring equipment at each location to measure the effectiveness over an entire year's worth of outdoor temperatures.

Of these 27 sites, 25 switched from a natural gas water heater to a 120V HPWH, giving us a considerable sample to understand the effects of 120V HPWHs as a fuel-switching measure. Our study participants reported 92% satisfaction with their new units overall, and the monitoring data found few issues with hot water availability, even at the coldest points in the year. Consumption levels were the best predictor of the hot water runouts that did occur. Households with the largest water consumption levels experienced the most runouts, and those houses had more runouts in the winter, when groundwater temperatures were lower.

The field study yielded important real-world data about what installers and distributors should consider when recommending a 120V HPWH for customers. We've put together an Installation Recommendations guide with our top-level findings.

Recommendations

• Utilities and manufacturers should consider 120V HPWH as a cost-effective retrofit solution in cold climates. Households in our study reported 92% satisfaction with their new units overall. These units save money operationally compared to gas units, and often save on install cost compared to 240V units. However, 120V HPWHs are significantly more expensive to install than gas units.
• Distributors should work with installers to have 120V units available for water heater replacements. These products are new to the market, and replacement is a good opportunity for homeowners to consider them.
• Installers should consider several factors, such as household size and consumption level, before recommending a 120V HPWH. See our two-page overview of 120V HPWH Installation Recommendations, which can help installers make a decision as to whether a 120V HPWH is a good fit and know what to do on installation day.

This research builds on prior research performed in California by the Advanced Water Heating Initiative (AWHI) and New Buildings Institute (NBI). See the results of that study here.