Compliance · Umweltbundesamt (DE)
Indoor CO₂ Guideline (German UBA / Pettenkofer scale)
Indoor air: ventilation adequacy guidance
Indoor carbon dioxide is not usually a direct toxic hazard at the concentrations found in occupied rooms; instead it is the classic proxy for ventilation adequacy. People exhale CO₂ continuously, so when it accumulates it signals that fresh air is not being supplied fast enough to dilute the other products of occupancy: odors, bioeffluents, and airborne pathogens. The reference point dates back to the 19th-century hygienist Max von Pettenkofer, who proposed a widely quoted indoor value of around 1000 ppm as the threshold of acceptable air. The German Federal Environment Agency (Umweltbundesamt, UBA) formalized this into a banded guideline that classes indoor CO₂ as hygienically acceptable, elevated, or unacceptable.
The standard
What the Indoor CO₂ Guideline Is
The guideline provides bands rather than a single hard limit, so that ventilation can be judged on a scale from good to poor. The banding is given in the limit table on this page.
Limit values
UBA CO₂ Limit Values
Every value Umweltbundesamt (DE) publishes for the parameter below, with its averaging period, as the standard states it.
Who it applies to
Who Uses It
Schools, offices, meeting rooms, lecture halls, gyms, and other densely occupied spaces use the CO₂ guideline to check that ventilation keeps pace with the number of people present. Facilities managers, building-services engineers, teachers, and occupational-health advisers use it to decide when to open windows, increase mechanical ventilation, or reduce occupancy. Interest broadened sharply after the COVID-19 pandemic, when CO₂ became a practical, inexpensive indicator of how well a room is ventilated and therefore of the risk of airborne transmission.
Monitoring
How Monitoring Demonstrates Compliance
Carbon dioxide is measured continuously with a non-dispersive infrared (NDIR) sensor, the reliable and stable method for indoor CO₂, and the reading is compared against the guideline bands in the limit table on this page. Because CO₂ rises and falls with occupancy through the day, continuous logging is what makes the guideline useful: a monitor shows the concentration climbing as a room fills and confirms that ventilation brings it back down. Carbon dioxide is one of the core parameters the Aethair family of indoor monitors measures in a single built-in device, so it is typically tracked alongside temperature, humidity, PM2.5, and TVOC, so ventilation adequacy and overall air quality show in one view.
Recommended
best match-
Aethair IAQ built-in sensors
Compact plug-in monitor with every sensor built in, nothing to add. Ideal for straightforward indoor air quality monitoring.
Built-inCarbon Dioxide (CO₂)Also measures 12 more
Formaldehyde (CH₂O)Dew PointHeat IndexRelative HumidityParticle Count (by size)PM1PM10PM2.5Total PM / Mass Conc.Barometric PressureAir TemperatureVOC (Total)
Alternative
Aethair PRO-
Industrial monitor for indoor and outdoor sites. Built-in sensors cover the essentials, and hot-swappable gas sensor cartridges and a differential-pressure option add more.
Gas 1
Aethair CO₂ (dual NDIR)
Carbon Dioxide (CO₂)Dual-thermopile NDIR (non-dispersive infrared) sensing measures CO₂ with no chemical consumables, for…
Also fits: Aethair CO₂ (self-calibrating NDIR)
Gas 2
Free: one more gas sensor cartridge
MultiSense
Free: a MultiSense, stock or built to order
Expansion
Free: differential pressure
Also measures 13 more
Dew PointHeat IndexRelative HumidityIlluminance / LightParticle Count (by size)PM1PM10PM2.5Total PM / Mass Conc.Barometric PressureEquivalent Continuous Level (Leq)Sound Pressure Level (SPL)Air Temperature
Who measures each parameter
| Parameter | Aethair PRO | Aethair IAQ |  External |
|---|---|---|---|
| Carbon Dioxide (CO₂) | CO₂ (dual NDIR), CO₂ (self-calibrating NDIR) cartridges | Built in | 2 instruments via Thiamis |
Devices
Devices That Cover UBA CO₂
How much of this standard one Aethair monitor covers, followed by the third-party instruments in the sensor catalog that measure its parameters. Each connects to Environet through a Thiamis gateway, which adds whatever the monitor leaves out.
Aethair monitors
Covers it on its own
Solutions
Solutions Judged Against UBA CO₂
HVAC & Building Management
Monitor ventilation and filtration, with data for your BMS
Indoor Air Quality
Offices, schools, homes, and public buildings
School Air Monitoring
Classroom CO₂, particulates, and campus IAQ
Questions
UBA CO₂ FAQ
Why is CO₂ used to judge ventilation rather than health?
At the concentrations reached in ordinary occupied rooms, CO₂ mainly indicates how much exhaled air has accumulated, which mirrors how much fresh air is being supplied per person. High CO₂ therefore flags inadequate ventilation (and the build-up of odors, bioeffluents, and potentially airborne pathogens) long before CO₂ itself would affect health.
What is the Pettenkofer number?
It is the roughly 1000 ppm indoor CO₂ value proposed by the hygienist Max von Pettenkofer in the 19th century as the threshold of acceptable indoor air. It remains the classic reference, and the UBA guideline builds on it by banding concentrations above and below it from acceptable to unacceptable, as shown in the limit table on this page.
Why did CO₂ monitoring become popular after the pandemic?
Because CO₂ is a simple, low-cost stand-in for how well a room is ventilated, and better ventilation lowers the risk of airborne disease transmission. Placing a CO₂ monitor in a classroom or office gives an immediate, visible cue to open windows or boost airflow when a space becomes stuffy.
How do I monitor indoor CO₂?
Use a continuous monitor with an NDIR CO₂ sensor placed at head height away from direct breath, logging through the occupied day. The Aethair family measures CO₂ alongside temperature, humidity, and particulates in one device. Use the configurator to choose the right configuration for your rooms.
Monitor Against UBA CO₂
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