Triac vs. relay thermostat: what are the differences?

Thermostats use two switching methods: the triac, precise and silent with short cycles, suitable for baseboards and convectors, and the relay, mechanical and noisy with long cycles, necessary for devices with motors or fans such as fan coil units. The triac ensures a stable temperature, while the relay protects the motor.

To control electric heating, thermostats use two different switching methods: triac or relay. Although their role is the same, their impact on your comfort and the lifespan of your devices differs.

The Triac: Precision and Silence

The triac is an electronic component that allows very fine energy management. Instead of turning the heating on for long minutes, it operates in very short cycles (about 15 seconds).

  • Temperature Stability: By sending energy almost constantly, it avoids temperature fluctuations. The heat in the room therefore remains stable.
  • Silent Operation: Since there are no mechanical parts moving inside the thermostat, the switching produces no noise.
  • Efficiency: This technology is the recommended standard for most residential electrical installations.

Recommended Use: Electric baseboards, convectors, and radiant ceilings.

The Relay: A Necessity for Motors

The relay is a mechanical switch. Unlike the triac, it operates with much longer cycles (about 15 minutes). Each time it activates or deactivates, you can hear a physical “click.”

While the triac is generally superior for comfort, the relay becomes necessary in one specific case: when the heating device has a motor or fan.

  • Motor Protection: The long cycle of the relay allows the motor to start and operate without premature wear.
  • Sound Constraint: The mechanical noise of the relay is normal but may be noticeable in a bedroom, for example.

Recommended Use: Only for fan coil units (air heaters).

Comparison Table

Characteristic TRIAC Switching RELAY Switching
Heating Cycle Short (15 seconds) Long (15 minutes)
Noise Level Silent Audible Click
Precision Almost no temperature fluctuations Perceptible temperature fluctuations
Compatibility Baseboards, convectors Fan coil units


Product models associated with this article:

  • (Wi-Fi) TH1123WF, TH1124WF, TH1133WF, TH1134WF, TH1133CR, TH1134CR, TH1143WF, TH1144WF, TH1500WF
  • (Zigbee) TH1123ZB, TH1124ZB, TH1134ZB/HC, TH1500ZB
  • (Others) TH1120RF, TH1121RF, TH1500RF, TH1120P, TH1120, TH1124NP

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