Question

Use CO2 as a ventilation clue, not a complete indoor-air-quality score

CO2 can tell you something about ventilation without telling you everything about the air.

When it fits

A CO2 monitor shows one number and you treat it as the health grade of the whole room.

When to avoid it

Building, combustion and infection-control concerns can require professional assessment beyond a consumer CO2 monitor.

A question to ask

Is the reading changing with occupancy or ventilation? · What is the outdoor/background context? · Could particles, VOCs, humidity or other pollutants matter independently? · What ventilation change can be tested safely?

Why it matters

ASHRAE's 2025 position document says indoor CO2 can be useful for understanding ventilation and occupancy, but acceptable IAQ depends on multiple pollutants and conditions. Use the trend as a clue—especially when people enter, windows close or ventilation changes—without declaring a room safe or unsafe from CO2 alone.

An example

A falling CO2 level after airing the room shows ventilation changed; it does not prove every pollutant is now low.

Check your result

CO2 informs a ventilation decision without becoming a universal air-quality verdict.

Keep this limit in mind

Building, combustion and infection-control concerns can require professional assessment beyond a consumer CO2 monitor.

Connected ideas

Evidence and sources

Supports

ASHRAE's 2025 position document treats indoor CO2 as a useful ventilation/IAQ indicator while emphasizing that IAQ depends on multiple factors.

Building, combustion and infection-control concerns can require professional assessment beyond a consumer CO2 monitor.

ASHRAE Position Document on Indoor Carbon Dioxide · See source record

All sources (1)

ASHRAE Position Document on Indoor Carbon Dioxide