A Marais-based deep-tech firm has just closed significant funding to decarbonise how European cities heat buildings—and it's drawing comparisons to the continent's most successful climate exits.
Thermex, a climate technology startup headquartered in the Marais district, announced a €12 million Series A round this week, marking a significant inflection point for Paris's increasingly competitive climate venture ecosystem. The funding, led by Breakthrough Energy Ventures and joined by localised VC firms including Paris-based Canopée and Copenhagen Climate Tech Fund, positions the three-year-old company as a serious contender in Europe's €85 billion annual heating market.
The company's focus is deceptively simple: replacing fossil-fuel boilers in European buildings with a hybrid system that optimises thermal energy storage and waste heat recovery. According to the International Energy Agency, heating and cooling account for roughly half of Europe's final energy consumption, yet the sector remains largely untouched by digitisation. Thermex's proprietary software integrates with existing infrastructure, reducing energy consumption by an average of 31 percent in pilot deployments across France and Germany—without requiring full system replacement.
Founded by three former researchers from the École Polytechnique and Mines Paris Tech, Thermex began operations from a co-working space on Rue de Turenne before relocating to a 800-square-metre office space near République Metro in early 2025. The startup currently employs 24 people, with plans to expand to 45 by year-end. Several team members previously worked at Neodyme, the French deep-tech accelerator housed in the 13th arrondissement.
The funding news arrives as Paris's climate tech sector experiences a notable maturation. Venture capital investment in European climate startups reached €9.2 billion in 2025—a 23 percent increase year-over-year—with France capturing approximately 18 percent of that total. Thermex's round underscore investor appetite for companies tackling what venture capitalists call "unsexy infrastructure" problems with measurable carbon reduction.
The Paris Chamber of Commerce and Industry has identified climate tech as a strategic priority, allocating €40 million in grants and co-investment funds through its Deep Tech initiative. Thermex's trajectory reflects a broader shift: whereas five years ago most French climate ventures focused on renewable generation, today's funding landscape increasingly rewards companies addressing energy efficiency in existing buildings—a far larger addressable market.
The startup's next milestone is signing its first municipal contract, likely in France or the Benelux region, by Q4 2026. Thermex has already completed technical audits with three regional heating authorities and is in advanced discussions with property management firms controlling over 200,000 residential units across Europe. If successful, the company could become another climate tech success story to emerge from Paris's bustling Marais district.
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