Symptoms
- Humidity percentage seems too high or too low
- Doesn't match a separate hygrometer
- Humidity control settings seem to trigger at odd times
Likely causes
- CommonPoor thermostat placement affecting humidity sensingHumidity sensors are sensitive to nearby moisture sources, drafts, and direct airflow.
- PossibleSensor calibration driftLike temperature sensors, humidity sensors can drift slightly out of calibration over time.
- PossibleDust or dirt on the sensorA dusty sensor can give a slow or inaccurate reading.
- PossibleConfusing indoor humidity with whole-house humidityA single-point sensor reflects only its immediate area, which can differ from the rest of the house.
What to do
- Compare the reading to a separate, inexpensive hygrometer placed near the thermostat.
- Check the thermostat's location for nearby moisture sources like a kitchen, bathroom, or humidifier vent.
- Remove the faceplate and gently clean dust from the sensor area with a soft brush.
- Check the settings menu for a humidity calibration or offset option and adjust it to match your reference hygrometer.
- If the thermostat controls a whole-house humidifier or dehumidifier, verify the target humidity level makes sense for your climate and season.
Tools and parts
- Separate hygrometer
- Soft brush
When to call a pro
Call an HVAC technician if the humidity reading stays far off after calibration and affects your humidifier or dehumidifier's operation.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.