CO2 Monitoring for Healthy Indoor Air

You can't see carbon dioxide (CO2), but your body definitely feels it. High levels cause headaches, fatigue, and poor concentration ("brain fog"). A CO2 monitor is like a speedometer for your ventilation—it tells you exactly when to open a window.

1. What is a Safe Level?

CO2 is measured in parts per million (ppm). Here is the breakdown:

• 400–450 ppm: Fresh outdoor air. This is the gold standard.
• 600–800 ppm: Excellent indoor air quality.
• 1000 ppm: The limit for good cognitive function. Above this, you might start feeling sleepy.
• 1500+ ppm: "Stale" air. Ventilation is urgently needed.
• 2000+ ppm: Common in crowded meeting rooms or small bedrooms at night. Causes headaches and significantly reduced focus.

2. Why Monitor CO2?

It is not just about staying awake. CO2 is a "proxy" for other pollutants. Since humans exhale CO2, high levels mean you are breathing air that has already been in someone else's lungs.

• Virus Transmission: High CO2 correlates with higher risk of airborne virus transmission (flu, COVID-19).
• Pollutant Buildup: If CO2 is trapped, so are VOCs (chemical off-gassing), dust, and humidity.

3. Choosing a Monitor (NDIR vs. eCO2)

Not all sensors are created equal. Be careful what you buy.

• NDIR (Non-Dispersive Infrared): The gold standard. It physically counts CO2 molecules using light. Accurate and lasts for years. (Recommended)
• eCO2 (Estimated CO2): Cheaper sensors that "guess" CO2 levels based on VOCs. They are often inaccurate. If you open a bottle of wine or use hand sanitizer near them, the reading spikes wildly. (Avoid)

4. Placement Matters

Don't put the monitor right next to a window (too fresh) or right next to your face (you will breathe on it and get a false high reading).

• Best Spot: Central location in the room, breathing height (seated or standing), away from direct drafts.
• Bedrooms: Place it on a dresser across the room, not the nightstand.

5. How to Use the Data

Don't obsess over the number; use it to build habits.

• The "Open Window" Threshold: Decide on a number (e.g., 1000 ppm). When it hits that, open a window/door for 5 minutes. Watch how fast it drops.
• Bedroom Test: Check the peak level in the morning. If it hit 2500 ppm overnight, you need to leave the door cracked open or run a fan tonight.

Summary

A CO2 monitor removes the guesswork. Instead of wondering if the air is stuffy, you know. It is the single most useful tool for learning how your home "breathes".