How to Calibrate the Shelly Plus H&T for Accurate Temperature and Humidity Readings

The Shelly Plus H&T is a reliable Wi-Fi temperature and humidity sensor, but environmental factors or sensor drift can affect its readings. Calibrating the sensor using the offset feature ensures you get accurate data for your smart home automations, whether you are controlling a heater, ventilator, or maintaining ideal plant conditions.

This step-by-step guide walks you through accessing the calibration settings in the Shelly app or web interface, adjusting temperature and humidity offsets, and following best practices to maintain accuracy over time.

Why Calibrate the Shelly Plus H&T?

Temperature and humidity sensors can deviate from true values due to manufacturing tolerances, placement near heat sources, or long-term drift. The Shelly Plus H&T allows you to apply a fixed offset – positive or negative – to both temperature and humidity readings via its web interface or mobile app. This means you can fine-tune the sensor to match a reference thermometer or hygrometer, ensuring your automations trigger at the right conditions.

If you rely on the Shelly Plus H&T to trigger a smart switch like the Shelly Plus 1 for ventilation or heating, even a one-degree error can lead to discomfort or energy waste. Calibration gives you peace of mind that your sensor is reporting accurately, making your entire smart home more efficient.

• Use a calibrated reference device (e.g., a thermocouple thermometer) to determine the current offset needed.
• Always allow the sensor to stabilize for at least 30 minutes in the environment before calibrating.

Accessing the Calibration Settings

Open the Shelly Smart Control app and select your Shelly Plus H&T device from the device list. Tap the gear icon for settings, then scroll down to the 'Calibration' section. There you will find two sliders or input fields: one for temperature offset and one for humidity offset. The offset value can be set in increments of 0.1°C and 0.1% RH respectively.

Alternatively, connect to the sensor's local IP address in a browser, log in, and navigate to 'Settings' > 'Calibration'. Both the app and web interface sync automatically, so changes made on one will reflect on the other. This flexibility makes it easy to calibrate even if you are not near your phone.

Setting the Temperature Offset

To calibrate temperature, first take a reading from a trusted reference placed next to the Shelly Plus H&T. Note the difference: if the sensor reads 22.5°C but the reference reads 23.0°C, you need to add +0.5°C offset. In the calibration screen, adjust the temperature offset accordingly. Positive values increase the reported temperature; negative values decrease it.

For example, if your sensor consistently reads 1°C low, enter +1.0 as the offset. The sensor will then report the corrected value. This is particularly useful when the sensor is used in a greenhouse or server room where precise temperature control is critical. Pairing it with a device like the Shelly EM Gen3 List for energy monitoring can help you track temperature-related energy usage and adjust settings automatically.

Setting the Humidity Offset

Humidity calibration follows the same principle. Use a reliable hygrometer or a salt test (e.g., 75% RH with NaCl solution) to determine the true humidity. Compare with the sensor reading and apply the offset. Humidity sensors can be more sensitive to drift, so periodic recalibration every few months is recommended.

If your Shelly Plus H&T reports 55% RH but the reference says 50% RH, set a humidity offset of -5%. The offset range is typically -20% to +20% RH. For critical applications like monitoring a wine cellar, humidor, or indoor plants, accurate humidity is essential to prevent mold or maintain proper moisture levels.

Best Practices for Long-Term Accuracy

Proper placement is key to maintaining accuracy. Avoid direct sunlight, drafts, or mounting near heat-generating electronics. The sensor should be mounted on an interior wall at about 1.5 meters height for room-level readings. Clean the sensor vents occasionally to prevent dust buildup that can insulate the sensor.

You can also cross-check with other Shelly sensors in the same area. If you have multiple Shelly Plus H&T units, you can calibrate them relative to each other. Additionally, integrating with smart switches like the Shelly 1 Mini Gen4 List allows you to create automations that respond to calibrated readings, such as turning on a fan when humidity exceeds a threshold.

• Recalibrate after a firmware update, as new firmware may affect sensor behaviour.
• Use the sensor's history logs in the app to spot long-term drift trends and recalibrate proactively.

Calibrating your Shelly Plus H&T is a simple process that dramatically improves the reliability of your sensor data. By applying the correct temperature and humidity offsets, your automations will trigger at the exact conditions you intend. For a complete smart home setup, consider pairing the sensor with other Shelly devices like the Shelly Plus 1 to control your appliances based on accurate readings.