Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.
Levels of indoor air quality (IAQ) as a function of the indoor–outdoor difference in CO2 concentration.
| IAQ Level | CO2,i–CO2,o Limits |
|---|---|
| I | CO2,i–CO2,o ≤ 350 ppm |
| II | 350 ppm < CO2,i–CO2,o ≤ 500 ppm |
| III | 500 ppm < CO2,i–CO2,o ≤ 800 ppm |
| IV | CO2,i–CO2,o > 800 ppm |
