Two masonry heaters for the Mermoz school complex in Rosny-sous-Bois

When the town of Rosny-sous-Bois built the Mermoz school complex, wood heating had a contract of its own: lot no. 14 — ‘Masonry heater’, won by Thermasse in 2021. Two heaters on the programme: one for the nursery school, the other for the leisure centre.

In a building that takes in young children, everything is designed for safety: radiant surfaces with controlled temperature, guard rails, controlled air supply, and fires run by staff when no children are present. At the nursery school, the heater core is a Brunner HKD 2.2 XL firebox, sized by design calculation.

A public contract runs over a long time — this one even more so, as it went through the health crisis: tender in 2021, weekly site meetings, coordination with the other trades, up to the final acceptance report signed in July 2025. With that experience behind us, the town also entrusted us with the heater at the école du Bois-Perrier — and the combined maintenance of the six Thermasse heaters it now owns.

A heater in a laboratory school

The Mermoz school complex is no ordinary project. Delivered in 2024 over nearly 3,800 m², it was designed and supervised by the town’s in-house project management team — its Research and Innovation department — and built with load-bearing straw bales, raw earth bricks and solid chestnut.

Heating is provided by the geothermal district heating network. The masonry heater has a precise place in it, which the project’s technical file puts this way: a choice of ‘low-tech, low-complexity systems’, alongside natural dual-flow ventilation coupled with an earth-air heat exchanger. In other words, a back-up with no electronics and no wearing parts, which keeps working whatever happens to the rest.

This is the logic behind the presence of masonry heaters in four schools in the town.