A Burgundy workshop where thermal engineering and masonry work at the same table: that is Thermasse. From the first line drawn to the handover report, everything comes from the same hands.
Hand and calculation
Everything starts with a design calculation, continues as a 3D drawing, passes through the workshop and ends trowel in hand at your home. No catalogue: each heater is born from the constraints and wishes of one particular house.
Guiom, the founder, holds the French vocational title of Mason and the Chimney Sweep and Flue Installer diploma from C.O.S.T.I.C. The company is qualified in masonry and in sweeping and flue work, covered by ten-year liability insurance (assurance décennale, mandatory in France), and holds RGE (French ‘reconnu garant de l’environnement’ label) Qualibois certification, Air module.
Where the idea came from
‘Long before I was a stove builder, one night on a trek at 4,000 metres, I heated stones in the fire and buried them under the tent so I could finally sleep warm. A masonry heater does nothing else: it stores the heat of a short fire in stone, and gives it back all night.’
— Guiom, founder
A role in the trade
Guiom is a founding member of the AFPMA, the Association Française du Poêle Maçonné Artisanal (French association of handcrafted masonry heaters), of which he has been president and where he now serves as treasurer on the board. In 2026, the heater built for the Bois-Perrier nursery school in Rosny-sous-Bois won both categories of the AFPMA photo competition — ‘best (unusual) photo’ and ‘most beautiful heater’.
Two houses, one fire
Thermasse designs and builds to measure. Cœur de Foyer, our retail brand, sells refractory materials, hardware and kits online, and publishes the video tutorials that guide self-builders. Want us to build it for you? That is Thermasse. Want to build it yourself, with proper support? That is Cœur de Foyer.
Eco-building as a heritage
Our practice extends to eco-building: load-bearing straw-bale walls (Nebraska technique), earth and lime-putty renders, interior architecture. The same hands, the same demands on materials.
In one sentence — Thermasse (Pouilly-en-Auxois, Côte-d’Or) has been building made-to-measure masonry heaters, calculated, hand-built in masonry and delivered with their documents, throughout France since 2010.
What we do not do
A company is also defined by what it refuses. Here are our four refusals, and they hold.
We do not sell heaters from a catalogue. Each heater is calculated for a volume, an insulation level and a way of life. A heater chosen from a photo is a badly sized heater half the time.
We do not install a heater we have not sized. Neither our own nor anyone else’s. Responsibility for a masonry structure weighing over a tonne cannot be split in half.
We do not promise to heat a poorly insulated house with a well-designed heater. When the calculation shows that insulation must come first, we say so — even if it pushes the project back a year.
We never show a computer-generated image and present it as a finished project. On this site, a photo of a heater is the photo of a heater that exists. When an image is a 3D render or a projection, it says so alongside.
Five facts, and the means to check them
- 357
- projects completed. The count comes from our own project files, one by one — not from an estimate.
- 187
- municipalities where we have worked, from the Ardèche to the Territoire de Belfort.
- 56
- documented projects published on this site, each with its technical specifications. Those you can open one by one.
- 10/21/626
- number of the founder’s French vocational title of Mason, issued by the Ministry responsible for Employment on 5 August 2010. Added to it is the Chimney Sweep and Flue Installer diploma from C.O.S.T.I.C.
- QB/48106
- RGE Qualibois Air module qualification number, verifiable in the Qualit’EnR directory with our SIRET (French company registration number), 528 048 069 00025.
Guiom, founder of Thermasse, is a founding member of the AFPMA, the Association Française du Poêle Maçonné Artisanal, of which he has been president and where he is now treasurer.