The core idea
Indoor carbon dioxide can indicate occupancy-related ventilation performance but is not a complete indoor-air-quality score.
How the mechanism works
People generate CO2; indoor concentration reflects occupancy, outdoor baseline, mixing and ventilation rate.
When it becomes relevant
Typical trigger: Occupied bedrooms, meetings or closed-window periods.
Evidence that supports this interpretation
- CO2 rises with occupancy and falls when ventilation increases
- Patterns repeat by room and time
- Outdoor reference is known
Evidence that weakens it
- Combustion or sensor error is suspected
- The reading is isolated and unrepeatable
- Occupancy timing does not fit
What this concept cannot prove alone
A single observation, image or meter reading cannot confirm the complete failure pathway. Use this concept to form better questions, compare alternatives and decide which safe observation would be most informative next.
Safety and professional boundary
Very high readings, combustion concerns or illness symptoms require ventilation and safety assessment rather than DIY interpretation alone.
Primary references for this topic family
These references ground the general building-science or safety context. They do not diagnose a specific house, replace local requirements or certify a repair.
