Indoor CO2 Ventilation Calculator
ASHRAE ventilation math is written for HVAC engineers. Enter your room size, how many people are in it, and how much fresh air gets in, and get the same answer in plain numbers. Nothing uploaded.
Result
Good — fresh airWhat this means
This room maintains good air quality at the entered occupancy and ventilation level.
CO2 Buildup and Indoor Air Quality
How ASHRAE Math Works
ASHRAE assumes that CO2 builds up from occupants' breathing, and ventilation removes it. At steady state (when CO2 stops climbing), the rate of CO2 generation equals the rate of removal. If you have 4 people in a 50 m3 room with 1 air change per hour, you generate CO2 at 4 units/hour and remove it at ~1 unit/hour, so CO2 piles up. More ACH or fewer people brings the steady state down.
Why CO2 Matters Beyond Oxygen
You won't suffocate from elevated indoor CO2 - you have plenty of oxygen. But above 1000 ppm, CO2 clouds your thinking measurably (it affects cerebral blood flow and pH). Schools and offices now track CO2 as a proxy for air freshness. Below 800 ppm is fresh outdoor air; above 1500 ppm, most people notice reduced focus. This tool estimates steady-state CO2 to help you gauge whether your room feels stuffy and needs more ventilation.
FAQ
What does ACH (air changes per hour) mean?
ACH is how many times the entire room volume of air is replaced with fresh air every hour. A sealed room might have 0.3 ACH (very little exchange). A room with good mechanical ventilation might have 6-10 ACH. Higher ACH means better air turnover and lower steady-state CO2.
Is 1000 ppm a safe CO2 level?
It's acceptable, but not ideal. Above 1000 ppm, cognitive performance and focus decline measurably, especially for students. Indoor air quality standards recommend keeping below 800 ppm in schools and offices for optimal alertness. Anything above 1500 ppm starts affecting most people noticeably.
How can I reduce CO2 in my room?
Increase ventilation: open windows, crack a door, turn on mechanical ventilation, or install a fresh-air system. Reduce occupancy per unit volume, or reduce time spent in the space. Adding plants or CO2 scrubbers has minimal effect - only ventilation with outdoor air works reliably.