Tasmota MH-Z19B CO2 Monitor

Tasmota MH-Z19B CO2 Monitor

Build a WiFi-connected CO2 monitor that measures indoor carbon dioxide levels using the MH-Z19B NDIR (non-dispersive infrared) sensor. Published via MQTT to Home Assistant for ventilation automation and air quality alerts.

Why This Project

• Indoor air quality — CO2 above 1000ppm causes drowsiness and reduced cognitive function
• Ventilation automation — trigger fans or open windows when CO2 is high
• NDIR technology — accurate, stable, long-lasting (no chemical sensor drift)
• COVID-era relevance — CO2 levels correlate with room ventilation quality
• 5-year lifespan — MH-Z19B has built-in auto-calibration

Components Required

Component	Purpose	Est. Cost
Wemos D1 Mini (or any ESP board)	WiFi microcontroller	$3
MH-Z19B (or MH-Z19C) sensor	NDIR CO2 measurement	$15-20
Jumper wires	UART connections	$0.50

Wiring (UART)

MH-Z19B          Wemos D1 Mini
───────           ─────────────
Vin           →   5V (sensor needs 5V!)
GND           →   GND
TX            →   GPIO14 (D5) — Tasmota RX
RX            →   GPIO12 (D6) — Tasmota TX

Important: The MH-Z19B requires 5V power (not 3.3V), but its UART TX output is 3.3V compatible with ESP8266/ESP32.

Tasmota Setup

1. Flash tasmota-sensors.bin (ESP8266) or tasmota32 (ESP32)
2. Configuration → Configure Module
3. Set GPIO14 to MHZ Rx
4. Set GPIO12 to MHZ Tx
5. Reboot — CO2 readings appear on the dashboard

Configuration Commands

# Set measurement range (default 2000ppm, max 5000ppm)
Sensor15 5000

# 3-minute warm-up time before first accurate reading
# Sensor auto-calibrates over 24 hours (ABC logic)

CO2 Level Reference

CO2 (ppm)	Level	Action
400-600	Excellent	Normal outdoor/well-ventilated
600-1000	Good	Acceptable indoor
1000-1500	Fair	Open windows, increase ventilation
1500-2000	Poor	Drowsiness, reduced concentration
2000+	Bad	Headaches, must ventilate immediately

Home Assistant Automation

automation:
  - alias: "High CO2 alert"
    trigger:
      - platform: numeric_state
        entity_id: sensor.tasmota_mhz19b_co2
        above: 1000
    action:
      - service: fan.turn_on
        target:
          entity_id: fan.ventilation
      - service: notify.mobile
        data:
          message: "CO2 is {{ states('sensor.tasmota_mhz19b_co2') }}ppm — ventilate!"

Compatible Boards

• Wemos D1 Mini — compact, widely available
• NodeMCU — if you need additional sensors alongside
• Any ESP32 board — add a display for local CO2 readings
• ESP-01S — possible but tight on GPIOs (uses TX/RX pins)