Underfloor heating (UFH) is standard in Central European residential construction. When combined with KNX zone control, it becomes a genuinely smart heating system — individual room setpoints, presence-based setback, integration with heat pump schedules, and accurate energy metering per zone.

UFH system overview

A typical wet UFH system: a manifold (Uponor, Rehau, Danfoss) distributes hot water to floor loops via electro-thermal actuators (24V or 230V). Each actuator is a normally-closed valve — when energised (24V applied), the valve opens and hot water flows through the loop. The heat source (gas boiler, heat pump) provides the hot water circuit. The pump runs continuously or on demand.

Zone control: thermostat to actuator

Each room zone needs: (1) a KNX room temperature sensor/thermostat, and (2) a KNX actuator output wired to the floor heating actuator. The KNX thermostat compares measured temperature to setpoint and outputs a 1-bit (on/off) or 0-10V signal to the actuator. For 1-bit: actuator is on (valve open) or off (valve closed). For PI control: the thermostat calculates how long the valve should be open in each cycle — this is called pulse-width modulation (PWM) control and provides more accurate temperature regulation.

Typical KNX devices for UFH

KNX thermostat with floor heating function (Gira Room Thermostat 2176.., MDT Room Controller). MDT AKU-1616.03 (16-channel output, 24V actuators). Alternatively: Hager TXA212B (12-channel 24V). One actuator output per zone. The manifold typically has 10–14 zones — so a 16-channel actuator covers it with spares.

Pump management

The heating pump should only run when at least one zone valve is open. Wire the pump to a KNX actuator output. Create a KNX logic: OR all zone valve states → if any valve is open → switch pump on. Add a 3-minute delay before turning the pump off (avoid hunting). The MDT Logikmodul or Home Assistant logic can handle this.

Setback scheduling

The real energy benefit: instead of running at 20°C continuously, implement: occupied 20°C, night 17°C, vacation 13°C. KNX weekly scheduler + presence detection (via motion sensors or phone-based presence) switches setpoints. For heat pump: coordinate the setback with the heat pump's own tariff schedule (night rate electricity).

Integration with heat pump Modbus

Most heat pumps (Daikin, Mitsubishi, Vaillant, Nibe) have a Modbus TCP/RTU interface. Read outdoor temperature, flow temperature, COP. KNX (via gateway) can request different flow temperatures based on outdoor temperature (weather compensation curve) — overriding the heat pump's built-in curve for finer control.

EN 15232 energy savings

Properly implemented KNX + UFH zone control delivers 15–30% heating energy savings compared to a single-zone thermostat. The biggest gains: night setback, presence-based setpoint reduction, and eliminating heating of empty rooms.