An ordinary home water heater could double as a small energy-storage device, no tank replacement required.
French climate-tech startup Elax Energy has raised €30 million ($33.5 million) to retrofit water heaters this way, saying the approach can help households cut water-heating costs by using cheaper, cleaner electricity.
For households, the appeal is straightforward: lower water-heating costs through smarter timing, and no changes to behavior needed.
Here's what to know
The startup says it can help homes use cheaper, cleaner electricity by retrofitting existing water heaters with connected thermostats. As VentureBurn reported, the company's funding round is meant to expand that model beyond social housing and into the much larger private residential market.
What makes the setup useful is that a hot water tank can hold onto the heat for hours. So, electricity used during sunny midday periods can still provide hot water later on, turning the tank into a simple form of heat-based energy storage.
Because the thermostat uses its own mobile connection, households do not need to connect it to home Wi‑Fi, per VentureBurn. Elax says installation takes about 20 minutes, and after that the device learns when a household typically needs hot water so it can move heating to cheaper, cleaner periods and away from inefficient ones.
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Households don't need to replace a functioning tank to take part. The savings come from smarter control of equipment many people already own.
More background
In France, the logic of off-peak power is changing. VentureBurn reported that the country is shifting discounted-rate hours to midday to absorb more solar output, making the old routine of heating water at midnight less useful than it was.
Its move into private homes comes after deployment in France's social-housing sector, where Elax had already equipped nearly 100,000 units. That gave the company a sizable real-world base for seeing how the hardware performs at scale.
An October flexibility pact put pressure on major energy players, including EDF and Octopus Energy, to manage equipment at scale, increasing demand for tools that can respond to fluctuations in renewable power, according to VentureBurn.
Elax worked with environmental consultancy Carbone 4 and says its technology can trim a home's water-heating energy use by 20% to 25%, potentially lowering bills without sacrificing comfort.
What's being done?
The company says the new funding will help it shift from institutional and social-housing deployments into private residences, where growth typically depends on consumer marketing and installation capacity.
Its backers include Crédit Mutuel Impact, Fonds Révolution Environnementale et Solidaire, and Noria, according to VentureBurn. The funding is intended to help the company broaden deployment while showing homeowners that the retrofit can produce measurable savings.
Rather than replacing boilers, Elax is trying to make existing ones smarter. By avoiding needless overheating and moving heating cycles into cleaner, lower-cost hours, the company is turning standard household equipment into a flexible grid resource.
As more midday solar power comes online, grids can direct some of that energy into hot water tanks already sitting in homes instead of curtailing abundant renewable electricity.
Where can I learn more?
Elax's retrofit is part of a push to make household water heating cheaper, smarter, and more responsive to the grid.
• Mixergy says smart hot water storage can cut household energy costs by 60%.
• Cala's heat pump water heater can shave nearly $500 off annual bills.
• Homeowners say Cala's smart water heater upgrade can deliver thousands of dollars in long-term savings.
• A high-tech water heater can save a household $2,100 over time.
• With rebates, an ultra-efficient water heater can be almost free to run.
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