Goals

  • Replicate original behaviour — 50/50 on and off, reversing direction every minute
  • Finer control than the 4 factory speed levels
  • Ventilate individual rooms — all but one fan running in the same direction
  • Extractor fan booster — all fans blowing inward (only works with an extractor that vents to the outside)
  • Silent ventilation for individual rooms (e.g. bedroom) — one fan off, all others running in the same direction
  • Higher maximum number of fans
  • Easier integration with Home Assistant

Controlling the Buderus decentralized ventilation unit with a Shelly for more flexibility.
The fan has 3 pins: +, − and PWM. The PWM signal behaves as follows:

Voltage Behaviour
0 V 100 % reverse
2.5 V standstill
5 V 100 % forward

Materials

  • Shelly Dimmer 0/1–10V PM Gen3 (not the Shelly Dimmer or the Shelly RGBW)
  • 230V AC to 12V DC 1A transformer
  • Buderus Logavent HRV126-43 D complete set
  • 2× Wago 3-way terminal block

Wiring

Wiring diagram

Diagram is AI-generated.

230V

  • 230V N → Wago1
  • 230V L → Dimmer L
  • Wago1 → Dimmer N
  • Wago1 → Transformer N
  • Dimmer O → Transformer L (allows cutting power to the transformer via the Shelly)

12V

  • Dimmer − → Wago2
  • Wago2 → Transformer −
  • Wago2 → Fan −
  • Dimmer + → Fan PWM
  • Transformer + → Fan +
Shelly Ventilator Wiring