Hang this poster beside the classroom CO₂ monitor, so anyone who reads the number knows what it means.
What is on the poster
What the reading means
| CO₂ reading | What it means |
|---|---|
| Below 800 ppm | Good ventilation: the air is refreshed with outside air regularly. |
| 800 to 1,100 ppm | Acceptable: ventilation is adequate under most conditions. |
| Above 1,100 ppm | Action needed. Over it more than once a week: improve the ventilation with qualified HVAC staff. |
Raise the clean air: the CDC target is 5 or more air changes an hour
- Bring in as much outdoor air as the HVAC system safely allows, at maximum for 2 hours before and after the building is occupied.
- Set the thermostat fan to ON, not AUTO, so air keeps moving through the filters.
- Use MERV 13 filters, or the highest rating the system runs without losing airflow.
- Run exhaust fans while the building is occupied and for 2 hours after, and check they exhaust outdoors.
- Still short? Add a HEPA air cleaner sized to the room: air changes = clean air delivery rate × 60 ÷ room volume.
- Open windows and doors only where it is safe, and with the facilities staff.
An air cleaner takes out particles; it does not bring CO₂ down. Never run a cleaner that makes ozone in an occupied room.
The poster's drawing shows a monitor reading 1,200 ppm on the scale: 400 is outdoor air, and 1,200 is about three times the outdoor level, a full class and too little fresh air.
Built to the Science Safety Teaching Standard
This poster carries the SSTS mark. Like every Science Safety course, it is built to the Science Safety Teaching Standard (SSTS): every rule on it is taken from the body that governs it, at its current edition, and the source is printed on the poster, so you can check it yourself.
Stay current
When you get this poster, it is saved to your Science Safety account. If we revise the poster, or the Ventilation Strategies module it comes from changes, we will email you, and the latest version will be waiting under Downloads in your account. Every revision carries its revision number and date at the bottom of the poster, so you can tell at a glance whether the copy on your wall is current.
Printing and hanging
- One-page PDF, US letter (8.5 by 11 inches).
- White background, so it prints clearly on any office or classroom printer without using much ink.
- Hang it beside the classroom CO₂ monitor.
- The QR code in the blue title band opens this page, so anyone can get their own copy.
- The QR code at the bottom opens the Ventilation Strategies module.
Learn more
The Ventilation Strategies module teaches the full topic this poster comes from.
Sources:
- Ventilation in Schools and Childcare Programs – CDC (NIOSH) (reviewed October 2, 2026)
- Ventilation FAQs – CDC (NIOSH) (reviewed October 2, 2026)
- How Much Ventilation Is Enough? – CDC (NIOSH) (reviewed October 2, 2026)
- Understanding Your Classroom CO₂ Sensor – UC Davis Western Cooling Efficiency Center (reviewed October 2, 2026)
- Guide to Air Cleaners in the Home – U.S. Environmental Protection Agency (reviewed October 2, 2026)
Poster SSP-0044, Rev. 1, October 2026.
