About 70  years have passed since highly energy-efficient heat pump water heaters (HPWHs) were introduced to the US market, having come to Europe even earlier. Market adoption has been promoted through extensive if not coordinated publicly sponsored R&D, demonstrations, energy-performance ratings, tax credits, utility rebates, regional initiatives, mandatory standards, whole-building electrification initiatives, and extensive advocacy.

Despite being cost-effective in most applications, the result has fallen far short of expectations, with HPWHs reaching only 1% of overall residential water heater sales, corresponding to 104,000 units sold into a total market of about nine million units in 2020, while still virtually unknown in commercial and industrial settings. There is evidence that premature commercialization resulted in market-spoiling that avoidably dampened consumer demand, even as the technology improved. US consumers have also faced a “boom-and-bust” environment—evidenced by many manufacturers entering and exiting the market.

This muted progress parallels a patchwork policy landscape and a host of persistent market barriers, both real and perceived. By contrast, the relative success of residential, commercial, industrial, and municipal HPWHs in many countries across industrialized Europe, Asia, and the Middle East has been accompanied by greater public–private coordination and more effective industrial policy and incentives.

Looking forward, water heaters are increasingly recognized as demand-flexible thermal “batteries” to allow more complete use of surplus renewable energy. This, together with a more focused and coherent policy strategy, may provide new opportunities in the USA for the technology to finally establish its value and make a material contribution to decarbonization.

Read the abstract and download Evan Mills’ full article in the journal Energy Efficiency.