Home Assistant Air Quality Sensors Guide: CO2, PM2.5 & Smart Automations

A 3-in-1 air quality monitor that tracks CO2, temperature, and humidity. It uses an NDIR CO2 sensor with a typical accuracy of ±50 ppm ±5%, helping you better understand indoor ventilation quality.

✅ Best for monitoring indoor ventilation in bedrooms, home offices, classrooms, nurseries, and other enclosed spaces.

Choose it if:
● You work from home and experience afternoon brain fog or headaches
● You want to know when a room needs fresh air ventilation
● You have multiple people in a closed space (meetings, classrooms)

Comparison at a Glance

 

Home Assistant Integration via Matter

Both Sonoff AirGuard PM and CO₂ monitors use the Matter-over-Wi-Fi wireless protocol, allowing them to be added directly to Home Assistant. A QR code on the back of each device enables quick setup through the Matter integration process.  

New to Matter? You can refer to the guide: How to add Matter devices to Home Assistant?

Home Assistant can monitor indoor air quality using CO₂, PM2.5, PM10, temperature, and humidity sensors. Once connected via Matter, Zigbee, or Wi-Fi, these sensors can display real-time data, track historical trends, and automate ventilation, air purifiers, and other smart home devices.  

Looking for Temperature & Humidity Sensors?

If your primary goal is monitoring indoor temperature and humidity rather than CO₂ or particulate matter, a dedicated temperature and humidity sensor may be a better fit.

SONOFF also offers several Home Assistant-compatible options, including: 

• SNZB-02DR2 – Zigbee sensor with a 3.6" large LCD and support for stand placement/hook hanging.
• SNZB-02D – Zigbee sensor with 2.5" LCD and support stand mounting.
• SNZB-02WD – IP65-rated Zigbee sensor with 2.2" LCD for indoor humid & wet environments.
• SNZB-02LD –  Zigbee sensor with  2.2" LCD  and a 1.5 m waterproof probe that reaches into liquids and enclosed spaces that the sensor body can't fit into (temperature only — no humidity sensor).
• SNZB-02P – Compact Zigbee sensor with no screen and up to 4-year battery life
• SNZB-02B – Zigbee sensor with no screen and slim design (only 27.8 mm wide and 20 mm thick) for narrow spaces

👉 Want to learn more? Check out our complete guide: Home Assistant Temperature & Humidity Sensor Setup and Automation Guide. 

 

Best Home Assistant Air Quality Automations

Connecting an air quality sensor to Home Assistant is only the beginning. By using real-time sensor data to trigger automations, you can automatically improve ventilation, control air purifiers, reduce excess humidity, and respond to changing indoor air conditions. Here are four practical automations that many Home Assistant users build.

Automatically Improve Ventilation Based on CO₂

High CO₂ levels usually indicate poor ventilation. Home Assistant can automatically improve airflow when indoor CO₂ rises above a defined threshold.  

Suggested CO₂ Thresholds:

Typical automation logic:

• When CO₂ > 1000 ppm → Turn on ventilation fan / HRV / HVAC → (Optional) Send a notification when ventilation starts
• When CO₂ < 800 ppm → Turn off ventilation

✅ Best for: Bedrooms, home offices, study rooms, nurseries, and meeting rooms.

Automatically Turn On an Air Purifier Based on PM2.5

Cooking, candles, fireplaces, and wildfire smoke can quickly increase indoor PM2.5 levels. Home Assistant can automatically run your air purifier whenever particle levels become unhealthy.  

Suggested PM2.5 Thresholds:

📘Note: The EPA's 24-hour National Ambient Air Quality Standard (NAAQS) for PM2.5 is 35 µg/m³, while the WHO recommends an even more stringent 24-hour average not to exceed 15 µg/m³.

Typical automation logic:

•  When PM2.5 > 35 µg/m³ → Turn on Air Purifier for 30 min → Send notification (optional): "PM2.5 elevated — air purifier activated"
• When PM2.5 < 12 µg/m³ → Turn off air purifier

✅ Best for: Homes with pets, families with children, allergy sufferers, homes near busy roads, kitchens, and homes in wildfire-prone regions.

🔔Tips: Add a minimum run time (e.g., 30 minutes) to ensure the purifier cleans the entire room.

Automatically Control Bathroom Exhaust Fans Using Humidity

High humidity after showering can lead to condensation and mold. Home Assistant can automatically control an exhaust fan to keep humidity within a healthy range.  

Suggested Humidity Thresholds:

Typical automation logic:

• When humidity level > 60% RH → Turn on bathroom exhaust fan → Send notification (optional)
• When humidity drops below 50% RH → Wait 10 minutes (to clear remaining moisture) → Turn off exhaust fan

✅ Best for: Bathrooms, basements, laundry rooms, and poorly ventilated spaces.

Note: The EPA recommends maintaining indoor relative humidity below 60%, ideally between 30% and 50%. 

Protect Your Home During Wildfire Smoke

Wildfire seasons are becoming longer and more severe, particularly across the western United States, Canada, and Australia. Even when windows are closed, fine particulate matter (PM2.5) from wildfire smoke can enter your home through ventilation systems and small air leaks.

If you live in an area affected by seasonal wildfire smoke, Home Assistant can help reduce indoor exposure by responding automatically when PM2.5 levels increase.  

Typical Automation Logic:

• When indoor PM2.5 rises rapidly → Turn on the air purifier → Switch the HVAC system to Recirculation Mode → Send an air quality alert.
• (Optional) If your home supports smart window actuators, automatically close windows during severe smoke events.

✅ Best for: Homes in wildfire-prone regions (California, Pacific Northwest, Canada, Australia), homes near forests or grasslands, and areas affected by seasonal smoke events.

🔔 Tips: Combine indoor PM2.5 monitoring with outdoor air quality data from AirNow or your local government air quality service. This allows Home Assistant to warn you before wildfire smoke significantly impacts your indoor environment.  

📖 Further Reading: During wildfire events, the U.S. EPA's Wildfires and Indoor Air Quality (IAQ) guide provides practical recommendations for reducing your exposure to wildfire smoke indoors, including using portable air cleaners, switching HVAC systems to recirculation mode, and keeping windows and doors closed.  

 

 

Conclusion

Indoor air quality isn't always visible—but with the right sensors, Home Assistant can automatically respond before poor air affects your comfort or health.

If your priority is improving ventilation, the SONOFF AirGuard CO₂ (SAWF-08P) helps monitor indoor CO₂ levels and trigger ventilation automations. If you're more concerned about cooking smoke, wildfire particles, or airborne dust, the SONOFF AirGuard PM2.5/PM10 (SAWF-07P) is a better choice for monitoring PM2.5 and controlling air purifiers. For the most complete indoor air quality monitoring, using both sensors together provides the widest coverage and unlocks the most useful Home Assistant automations.

Looking to monitor temperature and humidity instead? Explore our guide to Home Assistant temperature and humidity sensors to find the right sensor for your Home Assistant setup

 

 

 

FAQs

Q1: What is the best air quality sensor for Home Assistant?  

The best sensor depends on what you want to monitor.

• CO₂ sensors are ideal for improving ventilation, sleep quality, and productivity.
• PM2.5 sensors detect cooking smoke, wildfire particles, and other airborne pollutants.
• Temperature and humidity sensors help improve comfort and reduce the risk of mold.

If you're looking for Matter-compatible devices, the SONOFF AirGuard series integrates directly with Home Assistant over Matter.

 

Q2:  Should I choose a CO₂ sensor or a PM2.5 sensor?  

• Choose a CO₂ sensor if your goal is improving ventilation and indoor comfort.
• Choose a PM2.5 sensor if you want to monitor cooking smoke, traffic pollution, wildfire smoke, or other airborne particles.

For the most complete indoor air quality monitoring, many Home Assistant users use both.

 

Q3: How do I add an air quality sensor to Home Assistant?

The setup depends on the communication protocol.

• Matter → Add through Home Assistant's Matter integration.
• Zigbee → Pair using ZHA or Zigbee2MQTT.
• Wi-Fi → Use the manufacturer's integration or a compatible HACS integration.

Once paired, sensor entities can be used for dashboards, history, and automations.

 

Q4: Can Home Assistant automatically control an air purifier or ventilation system?

Yes. Home Assistant can use air quality sensor readings to automatically control air purifiers, fresh-air ventilation systems, HVAC equipment, bathroom exhaust fans, dehumidifiers, and notifications based on your own thresholds.

 

Q5: What CO₂ level is considered unhealthy indoors?

As a general guideline:

• Below 800 ppm – Excellent
• 800–1000 ppm – Good
• 1000–1500 ppm – Improve ventilation
• Above 1500 ppm – Poor ventilation; ventilate immediately 

Many Home Assistant users trigger ventilation automatically once CO₂ exceeds 1000 ppm.

 

Q6: At what PM2.5 level should I turn on an air purifier?

Many Home Assistant users automatically start an air purifier when PM2.5 exceeds 35 µg/m³, which aligns with the U.S. EPA's 24-hour PM2.5 standard.

If your household includes young children, allergy sufferers, or people with asthma, consider using a lower threshold.

 

Q7: Are indoor air quality monitors accurate?

Yes — provided they use quality sensors.

For the best accuracy:

• Choose NDIR sensors for CO₂ monitoring.
• Choose laser particle sensors for PM2.5 monitoring.

Consumer air quality monitors may not match laboratory equipment, but they are accurate enough for tracking trends and triggering Home Assistant automations.

 

Q8: Where is the best place to install an air quality sensor?

Install the sensor at breathing height in the room you want to monitor, away from windows, HVAC vents, direct sunlight, and the air purifier itself. This helps provide more representative readings of the air people actually breathe.