From water heater to thermal battery: a smart home upgrade

washington post

A California homeowner cut ties with his gas utility by converting his water heater into a thermal battery - slashing emissions, lowering bills, and storing energy at home.

When Ted Treadwell’s gas furnace and water heater neared retirement after 25 years, he saw an opportunity. Instead of replacing them with another gas system, the Santa Rosa homeowner installed an all-electric setup from Harvest Thermal that turns his water heater into a “thermal battery.”

The system uses a high-efficiency CO₂-based heat pump to heat water in a 119-gallon tank to 150°F. That tank stores enough energy to supply hot water and space heating for more than 24 hours. A smart controller manages the heat pump’s operation, running it when electricity is cleanest and cheapest.

“It’s a great system,” Treadwell said. “I wish more people knew about it.”

Thanks to solar panels on his roof and time-of-use electricity rates, Treadwell now receives credits from his utility - effectively getting paid to power his home. He expects to break even on the system in under 10 years.

The Bigger Picture: A Battery in Every Tank?

Water heaters consume a big chunk of residential energy. Retrofitting them into smart thermal batteries could help utilities balance the grid, reduce fossil fuel reliance, and save consumers money - especially during peak hours when electricity is most expensive.

Harvest Thermal’s system includes a heat pump, insulated water tank, and smart controller that predicts demand and adapts to real-time conditions. With incentives, systems can cost as little as $15,000, and reduce heating emissions by up to 90%.

Nonprofits like Peninsula Clean Energy are already supporting installations for low- and middle-income households, proving thermal batteries can replace traditional gas infrastructure at scale.

Is It Right for You?

These systems are best suited for homes under 3,000 sq ft in mild climates, especially when replacing both the furnace and water heater. Incentives like the federal 25D tax credit and California’s Energy-Smart Homes program can dramatically cut upfront costs.

“We’re future-proofing homes,” said Harvest Thermal CEO Jane Melia.

With gas prices rising and utilities shifting to time-based electricity pricing, thermal batteries offer both financial and climate resilience.

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