Underfloor heating

Underfloor heating (hydraulic) distributes heat through a low-temperature water network embedded in the screed. By radiating heat, it provides a uniform temperature, excellent comfort at low flow temperatures (approximately 30–40 °C), and very good efficiency with a heat pump or condensing boiler. When properly designed (insulation, installation, regulation) and correctly adjusted (weather compensation, hydraulic balancing), it reduces energy consumption and prevents excessively hot/cold zones.

Underfloor heating: principle and implementation

PE-RT/PEX tubes (usually Ø 12–20 mm) snake over a continuous insulation (under screed), then are embedded in a screed (cement/anhydrite) which stores and distributes heat (thermal inertia).

Key elements:

- Temperatures : starting low T° (30–40 °C), typical ΔT 5–10 K.

- Hydraulics : manifolds/manifolds with flow meters and balancing valves; variable displacement pump (VFD) recommended.

- Regulation : water law (slope/offset) + surface temperature limit (~28–29 °C in living areas). Outdoor sensors and sometimes ambient sensors.

- No installation : 10–20 cm depending on loads/insulations; limited loop lengths (pressure losses).

- Insulation : under screed and perimeter (decoupling strips), treatment of thermal bridges.

- Coverings : tiles/stone ideal; vinyl/wood compatible with underfloor heating (thermal resistance R ≤ recommended).

- Cooling (optional) : possible with heat pump and dehumidification; dew point sensor required to shut off before condensation.

Advantages, limitations and points to consider regarding underfloor heating

Interests

• Comfort: gentle radiation, no strong convection, high homogeneity.
• Energy: low temperature → COP PAC ↑ / condensation favoured on boiler.
• Aesthetics & acoustics: no visible emitter, quieter rooms.

Boundaries

• Inertia: slow reaction (anticipate via BMS and weather forecasting).
• Challenging coatings: limit the R-value of floors, take care with adhesives/undercoats.
• Subsequent drilling/modifications are more delicate (plans to be kept).

Points to consider

• Balancing: adjust flow rates per loop (flow meters), aim for a consistent ΔT.
• Regulation: gentle slope, fine offset; reasonable lowering to avoid yo-yo.
• Hydraulics: initial descaling, screen filter, air separator; thermal insulation of the manifolds.
• Expansions: expansion joints, respecting zones (max m²/length).
• Floor coverings: check compatibility with underfloor heating and overall R-value; avoid thick carpets.
• Cooling: dew point probe, adapted flow rates and temperature limits; humidity management (AHU/MVHR).

Anecdote — “The peaceful open-plan offices of Nantes”

In Nantes, newly built offices experienced alternating periods of intense heat in the morning and coolness in the afternoon. The underfloor heating system was unbalanced, the heating curve too steep, and the floor slabs very inert. The team adjusted the flow meters for each loop, reduced the slope, and activated a weather forecasting system (earlier restart, gentler power output). The result: stable temperatures, a comfortable feel, and the heat pump operating at a lower temperature most of the time.