Underfloor heating made from natural materials
The Lethermo system is an underfloor heating system based on natural materials – clay and wood, without adhesives. The clay panels hold the heating pipe, store the heat and release it evenly into the solid wood floorboards.
Low flow temperatures of 40 °C are enough to reach 48 W/m² – ideal for heat pumps. With a build-up height of just 45 mm, the system is also suitable for renovating older buildings. No screed, no long drying times.
At the end of its life, the system can be dismantled without destruction – the clay panels can be reused directly.
From the building site: the solid wood floorboards are screwed directly onto the fully laid Lethermo Floor system.
Lethermo Floor and N+F
The Lethermo Floor system is designed for solid wood floorboards on battens. The clay panels cover around 82% of the floor area and hold the heating pipe directly. The remaining floor area is filled with Lethermo's clay fill.
The N+F version (tongue and groove) works in a suspended floor – with or without battens. Both versions meet the DIN EN 1264 standard and achieve up to 48 W/m² with hardwood floorboards at a 40/30 °C flow/return temperature.
Lethermo Floor – clay boards on battens, heating pipe in the grooves, solid wood floorboards as the top layer.
Lethermo N+F – tongue-and-groove clay boards without battens, for the false floor (pugging level).
Lethermo Cera – N+F clay boards (tongue and groove), topped with unglazed clay screed tiles as a dry screed for tiles and natural stone.
Lethermo Cera – for tiles and levelled floors
If you don't want to lay solid wood floorboards, you can finish the Lethermo system with the Cera screed-tile layer. The unglazed screed tile distributes the load and the heat, creating a level base for tiles or natural stone.
The build-up for tiled floors:
- Lay Lethermo N+F clay panels on a Gutex Thermofloor or a hemp fleece (impact sound insulation) – connected via tongue and groove and laid with staggered joints.
- Insert a separating layer (paper)
- Lay Lethermo Cera screed tiles as a dry screed, fixed with Cera screed-tile adhesive
- Tiling directly with the Kholao Colle lay on the clay screed tiles
The Cera accessories – screed tiles and screed-tile adhesive – are perfectly matched to one another.
How installation works
- Prepare the substrate – determine the build-up height, lay a moisture barrier if needed, fit the edge insulation strips, then add the levelling fill and lay the impact sound insulation.
- Lay the clay panels – Floor version with battens; N+F version without battens, connected directly via tongue and groove.
- Insert the heating pipe – into the grooves of the clay panels, connected to the heating circuit manifold by a qualified installer, including a pressure test.
- Lay the floor covering – Floor/N+F: solid wood floorboards directly onto the battens; for tiles: lay Lethermo Cera screed tiles as a dry screed on the N+F panels.
The solid wood floorboards are screwed directly onto the battens – no screed, no drying time.
For solid slabs and timber joist floors
Whether a solid floor slab or a timber joist floor in an older building: a levelling layer of load-bearing dry fill or clay blocks, combined with wood fibre insulation, creates a level, sound, load-bearing substrate for the Lethermo Floor system. The build-up height remains low, and the floor gains additional mass for sound insulation and heat storage.
On a solid ceiling: loose clay chippings fill, two-layer wood fibre insulation, Lethermo Floor with heating pipe, solid wood floorboards.
On a timber joist ceiling: clay bricks and wood fibre insulation as a levelling layer, with the Lethermo Floor system on top.
Heating and cooling with one system
The Lethermo system can not only heat but also cool in summer – through the same heating pipe, simply using cold instead of warm water. This requires a heat pump that can also actively cool. It is designed according to DIN EN 1264-3 with dew point control, so no condensation forms on the floor.
- Cooling capacity at standard temperature difference (8 K): approx. 20–24 W/m² (depending on floorboard type), at 70 mm laying spacing
- A dew point sensor with control unit is required – reliably prevents condensation
- Same installation as for heating mode – no additional pipe system required
Comfortable warmth on solid wood flooring – warm in winter, pleasantly temperate in summer.
Technical data
| Dimensions (L × W × H) | 358 × 250 × 45 mm (± 2 mm) |
|---|---|
| Weight | approx. 75 kg/m² |
| Compressive strength | 12.3 N/mm² |
| Heat output (40/30 °C, 70 mm) | 48 W/m² (hardwood) |
| Heat output (40/30 °C, 140 mm) | 32 W/m² (hardwood) |
| Heat output (45/37 °C, 70 mm) | 68 W/m² (hardwood) |
| Heat output (45/37 °C, 140 mm) | 44 W/m² (hardwood) |
| Max. heating circuit | 8.5 m² (70 mm) / 17 m² (140 mm) |
| Heating pipe | PE-RTII/AL/PE-RTII, 14.4 × 2.2 mm |
| Pallet | 12.88 m² / EURO pallet |
| Standard | DIN EN 1264 / DIN EN 1264-3 (cooling) |
Advantages at a glance
- pure clay panels – completely natural materials
- Low flow temperature – ideal for heat pumps
- Suitable for renovation and new builds – only 45 mm build-up height, no screed
- Reversible – can be removed without damage, reusable or dismantlable into single-type materials
- Cooling possible – heating and cooling with one system
- Room climate – humidity regulation, impact sound reduction
- DIN EN 1264 certified
Frequently asked questions
How high is the build-up height?
Just 45 mm (± 1.5 mm) – also suitable for renovating older buildings. Impact sound insulation is not yet included. Good impact sound protection can be achieved with a 5 mm hemp fleece or a Gutex Thermofloor panel.
Is the system also suitable for tiled floors?
Yes, via the Cera version with screed tiles as a dry screed. The screed tiles form the dry screed that serves as the base for your tiles.
Can the system also cool?
Yes – provided a heat pump capable of cooling is available. See the "Heating and cooling with one system" section.
How humid should/must the room be during installation?
Before laying the floor covering, the heating should run for a few days until a relative humidity of 45–55% is reached (check with a hygrometer).
Is the system reversible?
Yes – the clay panels are dismantlable into single-type materials and reusable, with no bonding to the substrate.