ASHRAE humidity recommendations for reopening schools and universities.


ASHRAE (American Society of Heating, Refrigeration, and Air Conditioning Engineers) is a global company founded in 1894 that promotes human well-being through sustainable technologies for the built environment.

The ASHRAE Epidemic Task Force has recently published guidance on the operation of HVAC systems in schools and universities, to mitigate the airborne transmission of SARS-CoV-2. This is in preparation for the reopening of schools in the new academic year. The ASHRAE recommended winter classroom design condition specifies 40-50%RH through proactive humidification, either via AHUs or directly in the classroom.


Dave Marshall-George, UK Sales Manager at Condair plc, comments:


“It is very reassuring to see the guidance of an authority such as ASHRAE to keep a minimum humidity level of 40% inside buildings. Limiting the spread of infections by maintaining a humidity level above 40% rh has been proven in many scientific studies. ASHRAE has taken this very positive step in recognizing these scientific findings and specifying that humidifiers should be used in educational institutions during the cold season for the health and protection of students and staff.

Educational establishments, such as schools and universities, are key battlegrounds in preventing the spread of COVID-19, or other respiratory infections, such as the flu. Proper humidification during the cold season is an effective weapon against respiratory infections. Maintaining a humidity level of 40 – 60% rh helps the respiratory immune system to function efficiently and reduces the lifespan of airborne viruses.

We hope to see this recommendation taken seriously by the authorities. Similar advice from CIBSE in its COVID-19 Ventilation Guidance states that “relative humidity should be maintained above 40% rh”. The commercial humidifier production sector is ready to step up and play its role in the fight against COVID-19, but educational institutions must act now. We work frequently with universities to humidify research laboratories, archives and offices, but humidity control in classrooms is rarely implemented.

Humidification is a practical, natural and non-pharmaceutical intervention against respiratory infections and we hope to see similar and clear instructions for healthcare facilities and office buildings soon. ”


3 benefits obtained by maintaining a healthy humidity level.


1. Optimal functioning of the respiratory immune system.


Breathing dry air below 40%RH dries the mucous layer in our nose and throat. Thus it becomes less effective at capturing and clearing airborne pollutants and microbes, which in turn leaves us more susceptible to infections.



We are protected from infections by the self-cleaning mechanisms used by the mucous membranes of the airways. The surfaces of these mucous membranes are covered by fine motile hairs (cilia), which move freely inside a fluid secretion (saline layer). Above the saline layer is a layer of sticky gel, on which most viral, bacterial particles and inspired pollutants remain blocked. As long as the cilia remain very mobile, they can transport the secretions together with these microorganisms to the larynx, where these secretions can then be swallowed or coughed up from the respiratory tract.


2. Reduced quantity of airborne viruses.



When infected people breathe, talk, cough or sneeze, they release particles that contain potentially infectious viruses into the air. The smaller these particles are, the longer they can survive in the air. Airborne viruses survive for longer periods of time in a dry air environment. Proper air humidity control makes these infectious particles settle on surfaces faster, thus shortening the amount of time they spend in the air.


3. Airborne viruses are less infectious.



Employing commercial humidifiers to maintain a building’s indoor humidity throughout the winter is a practical solution to reducing seasonal airborne respiratory infections. Commercial humidifiers can supply moisture either to a central air handling unit in a building’s plant room or directly to a room’s atmosphere. Humidifiers deliver moisture to an atmosphere by either boiling water to create steam, creating a fine mist that rapidly evaporates, or by directly evaporating moisture from a wetted surface.



Condair offers complete humidification solutions using vaporization, evaporation, atomization, hybrid humidification, humidification and cooling technologies, water treatment systems and dehumidification solutions. If you are looking for a humidifier, do not hesitate to contact us, our team of professionals is ready to answer any question.

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