Metriot's OpenTherm Controller Makes Espressif ESP32, ESP8266 HVAC Control as Easy as Possible

Energy-monitoring smart home specialist Metriot has launched a compact controller board designed to adhere to the OpenTherm standard, allowing for heating, ventilation, and cooling (HVAC) control from an Espressif ESP32 microcontroller.

"Building your own thermostat is fun," Metriot's founder Jeroen Döll explains of the reason for the board's creation. "I wanted to safe money and reduce my CO₂ footprint by lowering central heating temperatures and thus making a HR condensing boiler more efficient."

The resulting board is designed for use with an OpenTherm-compatible Espressif ESP32 and ESP8266 firmware, providing control of compatible condensing boilers or air conditioning systems. Metriot's board itself doesn't include the microcontroller; instead, it provides what you need to connect the ESP32 or ESP8266 to the HVAC system without blowing anything up.

"With this board you can control your OpenTherm-enabled boiler or HVAC over Wi-Fi or Bluetooth, or integrate your boiler or HVAC with home automation systems like Tasmota, OpenHAB, Domoticz, or Home Assistant," Döll explains. "[It] should also work with ESP8266 and Arduino boards. It comes with programs to test the connection with your boiler, a full functioning basic thermostat example and a Arduino library designed in OSI model layers."

The board is now available on the Metriot Tindie store for $20, with the firmware and sample programs available on GitHub under the reciprocal GNU General Public License 3. Döll has also confirmed he is working on MQTT and web server sample projects, and notes that the board is designed to be breadboard-friendly for testing.