News, infographics and scientific mediation on indoor air renewal.
This web-site is designed to raise awareness of the importance of good air renewal in enclosed spaces.

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Click on an image below to download a PDF format of an infographic. The infographics and documents provided by letsair.org are licensed under a Creative Commons BY: credit must be given to the creator

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Ventilation matters - Discover why clean indoor air is vital to health


To discover why clean indoor air is vital to health, we recommend the website of National Engineering Policy Centre of United Kingdom. It's a very attractive and interactive site for understanding the basics of ventilation in enclosed spaces : natural or mechanical ventilation, air cleaning, CO2 monitoring... Follow the link below.

Scientific Mediation

Below, you'll find scientific mediation documents on the transmission of respiratory pathogens.

Version 2.50 / 2025-06-26

Version 2.44 / 2025-06-16

Version 1.00

Version 0.99

Indoor Air Quality Pioneers


By the 19th century, the importance of good air renewal in enclosed spaces was well known. And we even knew how to measure it, thanks to CO2. The limits recommended at the time are similar to those recommended in 2024. All this has been well known for a century and a half.

In the 19th century, school buildings were constructed to comply with hygiene regulations and promote the circulation of fresh air and light. In the 20th century, buildings were progressively constructed more for practical reasons and to be easy to heat, with poor air renewal.

Some theatres, the first in the late 19th century, also developed highly efficient ventilation systems with fresh-air intakes under the audience seats.

CO2 monitoring

Measuring CO2 is a simple, effective and inexpensive way of monitoring the quality of indoor air renewal in enclosed spaces. We offer examples of CO2 measurements in more or less well-ventilated premises, an easy-to-use ventilation simulator and the "air-score" as an indicator of this indoor air renewal quality.

CO2 monitors Buying Guide

Over the last 3 years, we have tested 30 models of CO2 monitors and we have selected products that we consider to be «best in class» in three categories. This choice is based on tests carried out on receipt of the equipment. The products we present meet all our requirements. Other products, sometimes less expensive, exist and can perform sufficient functions for certain uses. We have no links of interest with any of the above manufacturers.

Versatile


This versatile model is much appreciated by its users. It is often cited as a benchmark and could be described as the "iPhone" of CO2 monitors. Configuration on the device via micro-switches or via the app and bluetooth is quick and easy. Suitable for mobile or static use with an autonomy of several months.. It's a worthwhile investment.
Connected


This model is perfectly suited to the deployment of a connected monitors fleet in a building, a school for example. Its LORA connectivity means it's up and running straight out of the box and you can view the measurements on a pre-configured website. Once the device is connected to the app, you can change the settings very easily. Its battery will last for several years.

Decentralized Ventilation

If you want to quickly improve the quality of indoor air renewal in a confined space, such as a classroom, you can install decentralized ventilation. Some models are specifically designed for high-occupancy spaces, such as classrooms. Below are some products we haven't tested but that we think might be interesting

An excellent introduction to decentralized mechanical ventilation has been produced by the company BreathingBuildings in this document: Ventilation for Schools.

A shot video by the company AIRFLOW presents their solution: Airflow Susurro Decentralised MVHR

 Up to 1700 m3/h

 Up to 1000 m3/h

 Up to 920 m3/h

 Up to 4000 m3/h

 Up to 1500 m3/h

 Up to 2000 m3/h

Early adopters

Around the world, we can find places where indoor air renewal quality is monitored and CO2 levels displayed. Below, examples. And in Boston, Lübeck and Latvia, CO2 levels of classrooms and social centers can be freely consulted in real time on web dashboards. A remarkable effort of transparency.

Around the world


 
Boston, USA
CO2 monitors in 4322 classrooms


 
Lübeck, Germany
CO2 monitors in 2200 classrooms and 28 nurseries


 
Latvia
CO2 monitors in 14000 classrooms / 875 schools and social centers


 
Yokohama, Japan
1999 CO2 monitors in classrooms


 
Paris-Saclay Univ. Lending Program


 
US & Canadian libraries Lending Program


 

Metrics and Regulations

what is the correct metric for measuring air renewal in an enclosed space? Here are some answers and some informations or documents related to legal regulations or guidelines related to these metrics and Indoor Air Quality, particularly in schools.. You can also consult Joey Fox's excellent site or this article.

Do It Yourself


This is a prototype designed by students for children. The color indicates the air renewal quality. When the spout is pressed, Jasper announces the CO2 level. It's not commercially available.

This model, derived from the "RINOLFI" design, requires only 2 components, 4 wires, 8 solder joints and 2 3D printed parts. The cost is less than 50€.

miscellaneous

Work in progress : risk assessment

Below, we publish some infographics and we list the bibliographical references that will be useful to us in carrying out a future scientific mediation campaign on the assessment of the risk of airborne transmission. Please feel free to add to this list by sending an email to info@letsair.org

Risk Calculators

Research Papers

Contact

This page is maintained by Pascal Morenton, expert for a statement of the French High Council for Public Health (Haut Conseil de la santé publique) related to CO2 monitoring. You can contact Pascal at pascal.morenton@letsair.org.

This page and its documents were created with the help of many people through social networking contacts. The scientific mediation initiative is currently held by a multi-disciplinary group including clinicians, virologists, pneumologists, pediatricians, epidemiologists, aerosol specialists, engineers, scientific mediators, etc.