Virus lingers in still air
The virus that causes COVID-19 spreads mainly through respiratory droplets, which can linger in the air for hours after an infected person has left the room. Good ventilation can lower their concentration in the air, and with it the risk of infection for everyone else.
Open a window
Outdoor air comes in through open windows and doors, exhaust fans and well-maintained air conditioning. The risk of infection is higher in crowded indoor spaces. An open window is the cheapest practice on this site.
Is the window enough?
With a window open, is the air actually fresh? You can’t smell it, but a CO2 monitor turns the guess into a number you can watch fall. Breath is the main source of CO2 indoors, so the number shows how much of the room’s air has already been breathed. Outdoors it reads about 420 ppm. A steady reading under 800 ppm (opens in a new tab) likely means a well-ventilated room, and one consistently above 1,500 ppm (opens in a new tab) means poor ventilation.
The number is a guide, not a safe line. It doesn’t measure infection, and limited direct evidence (opens in a new tab) links CO2 levels to infection risk.
- NDIR monitors measure CO2 directly. Sensors sold as “eCO2” or “CO2 equivalent” guess from other gases and can be very inaccurate (opens in a new tab).
- Head height reads truest, at least 50 cm from windows, doors, vents and people.
- A falling number means fresh air is coming in.
- It can’t see air cleaners. HEPA purifiers and far UV-C lamps leave CO2 unchanged.
Videos
COVID-19: Clearing the Air Effectively - NHK WORLD-JAPAN (opens in a new tab)
New research shows how effective air circulation can reduce the risk of coronavirus infection.
Coronavirus: New Facts about Infection Mechanisms - NHK Documentary (opens in a new tab)
New research reveals how tiny droplets carrying the virus can stay in the air for some time. Watch the full documentary on NHK WORLD-JAPAN (opens in a new tab).
The research
17 papers chosen for this practice, each with its source and summary. After them, every study in the database that mentions room ventilation.
The review highlights the critical role of heating, ventilation, and air conditioning (HVAC) systems in controlling the spread of COVID-19, emphasizing the need for improved air filtration and ventilation strategies to ensure indoor air quality and reduce infection risks.
Key points
- HVAC systems can contribute to the spread of COVID-19 if not properly managed.
- Indoor air quality is crucial; ventilation can dilute airborne pathogens.
- Upgrading filters to MERV-13 is recommended to reduce virus transmission.
- Continuous operation of HVAC systems is essential for maintaining air quality.
- Outdoor air circulation before and after occupancy can mitigate risks.
- Portable HEPA air cleaners can supplement ventilation in poorly ventilated spaces.
- Avoid recirculation of air in HVAC systems to prevent airborne transmission.
- Regular maintenance of HVAC systems is necessary to ensure effectiveness.
- Implementing UVGI can enhance air disinfection but should not replace filtration.
- Social distancing and mask-wearing are still critical alongside ventilation strategies.
Air Cleaners, HVAC Filters, and Coronavirus (COVID-19) (opens in a new tab)
Using air cleaners and HVAC filters can help improve indoor air quality and reduce airborne viruses, but they should be part of a broader strategy that includes proper ventilation and other health precautions, especially for preventing the spread of COVID-19.
Key points
- Portable air cleaners can help improve indoor air quality, especially when ventilation is limited.
- Air cleaners alone cannot ensure safety from COVID-19; they should be used with other precautions like masks and social distancing.
- Choose air cleaners that are HEPA rated or have a high CADR for smoke.
- Place air cleaners in rooms where people spend the most time, especially if someone is vulnerable or isolating.
- Avoid using air cleaners that generate ozone in occupied spaces.
- DIY air cleaners can be effective but are not a permanent substitute for commercial options.
- Regularly check and replace filters in air cleaning devices.
Improving ventilation in elementary school classrooms can significantly reduce student absences due to illness, while higher levels of indoor air pollution are associated with more frequent absences.
Key points
- Higher classroom ventilation rates reduce illness-related absences.
- Increased indoor PM2.5 levels are linked to more illness-related absences.
- Mechanically ventilated classrooms benefit from controlling indoor particles.
- Improved ventilation and lower PM2.5 can enhance attendance and reduce health risks.
Improving indoor air quality through proper ventilation, filtration, and monitoring can significantly reduce the risk of COVID-19 transmission and other respiratory illnesses.
Key points
- Proper ventilation and air filtration are crucial to prevent COVID-19 spread indoors.
- Disinfecting surfaces is less effective than improving air quality.
- COVID-19 primarily spreads through inhaling aerosols, not surface contact.
- Regularly replacing indoor air can dilute virus concentration.
- HEPA filters and high MERV-rated filters are recommended for effective air purification.
- Monitoring CO2 levels can indicate air quality and ventilation effectiveness.
- Germicidal UV lights can help kill airborne viruses but must be installed correctly.
- Economic costs of infections can outweigh the costs of implementing air quality controls.
Coronavirus disease (COVID-19): Ventilation and air conditioning (opens in a new tab)
This article provides information for the general public on how proper ventilation and air conditioning can help prevent the spread of COVID-19 in homes, offices, schools, and airplanes.
Key points
- Ventilation is an important factor in preventing the spread of COVID-19.
- Natural ventilation is preferred over mechanical ventilation.
- Air conditioning can be used safely with proper maintenance and regular cleaning.
- High-efficiency particulate air (HEPA) filters can be used to improve air quality.
- When traveling on airplanes, wearing a mask and following recommended ventilation measures can reduce the risk of COVID-19 transmission.
COVID-19 and importance of air filtration (opens in a new tab)
Air filtration, avoidance of recirculation of air, enhanced particle filtration by suitable air filters, and air disinfection can control COVID-19 infection transmission in indoor spaces, and the use of HEPA filters, UVC light, and natural ventilation are effective methods for reducing the spread of the virus.
Key points
- Effective ventilation, avoidance of recirculation of air, enhanced particle filtration by suitable air filters and air disinfection can control COVID-19 transmission.
- Opening windows can increase natural ventilation and dilute indoor air, reducing infection spread.
- Indoor air purifiers with high efficiency particulate air (HEPA) filters can filter contaminated indoor air, but must be replaced regularly.
- Far-UVC light is recommended for single rooms without air conditioning, while a combination of HEPA filter and UVC light can reduce bacterial and virus load significantly in air-conditioned rooms.
- The supply or outdoor air should be filtered by a filter and then mixed with the recirculated air and supplied to the room through the HEPA filters.
- The ASHRAE recommends HVAC systems with a minimum efficiency of Minimum Efficiency Reporting Value-13 (MERV-13) to filter even very small particles.
Show all 17 papersShow fewer papers
Effects of ventilation on the indoor spread of COVID-19 (opens in a new tab)
This article discusses the importance of building ventilation in reducing the risk of indoor transmission of COVID-19, and explains how airflows can affect the spread of the virus. The authors suggest that high levels of CO2 can be used as an indicator of the potential presence of the virus in the air, and that poor ventilation can contribute to the transmission of other airborne diseases as well.
Key points
- COVID-19 can spread through the air indoors.
- Proper ventilation can help reduce the spread of COVID-19.
- Heavy breathing, coughing, and talking can expel droplets that contain the virus.
- These droplets can travel farther than 6 feet and can remain in the air for several minutes.
- The risk of transmission is higher in poorly ventilated indoor spaces.
- CO2 sensors can be used to monitor ventilation.
- The WHO recommends increasing ventilation and avoiding recirculation of air in public spaces.
How to improve indoor air quality, from filters and purifiers to HVAC upgrades (opens in a new tab)
Indoor air quality can have significant impacts on health, and there are various steps individuals can take to improve it, including increasing ventilation, controlling sources of pollutants, and using air purifiers or upgrading heating, ventilation, and air conditioning systems.
Key points
- Poor indoor air quality can contribute to health problems.
- Fresh air from outside is better than no fresh air from outside.
- Certain gases can be dangerous too, such as carbon monoxide and radon.
- Consumer goods and cleaning supplies can release pollutants like formaldehyde, benzene, and other volatile organic compounds.
- Smoking or burning a fire indoors introduces smoke.
- Poor indoor air quality can have health consequences that range from irritation of the eyes, nose and throat to headaches and dizziness to asthma attacks. It’s also linked to respiratory and heart disease.
- There may be cognitive risks to breathing polluted air as well.
- A portable air purifier can be a good way to clean the air if outdoor air quality is poor.
- The spread of airborne germs is a serious issue indoors.
- Ventilation, source control, and filtration can help improve indoor air quality.
- Schools, health care facilities, and group residential or care facilities are in the best position to benefit from air quality improvements.
Improving Ventilation in Your Home (opens in a new tab)
Improving ventilation in your home by bringing in fresh air, filtering the air, and improving air flow can help reduce virus particles and prevent the spread of COVID-19.
Key points
- Ventilate your home by getting fresh air into your home, filtering the air that is there, and improving air flow.
- Good ventilation, along with other preventive actions, can help prevent you and others from getting and spreading COVID-19 and other respiratory viruses.
- Here are some ways you can improve ventilation in your home: bring as much fresh air into your home as possible, filter the air in your home, consider using a portable air cleaner, turn on the exhaust fan in your bathroom and kitchen, use fans to improve air flow, and limit the number of visitors in your home and the time spent inside.
Indoor Air Changes and Potential Implications for SARS-CoV-2 Transmission (opens in a new tab)
Increasing ventilation and filtration in indoor spaces can help reduce the risk of airborne transmission of infectious agents, including SARS-CoV-2, and should be considered as a fundamental part of risk reduction strategies.
Key points
- Increasing air changes per hour and air filtration can help reduce the risk of airborne transmission of respiratory infectious diseases like SARS-CoV-2.
- Higher ventilation and enhanced filtration are often overlooked but fundamental parts of risk reduction strategies that could have benefits beyond the current pandemic.
Physical interventions to interrupt or reduce the spread of respiratory viruses (opens in a new tab)
This article explores different physical interventions that can be used to interrupt or reduce the spread of respiratory viruses, such as wearing masks, social distancing, and improving ventilation.
Key points
- Physical interventions can help reduce the spread of respiratory viruses.
- Examples of physical interventions include wearing masks, social distancing, and hand hygiene.
- These interventions can be effective in reducing the transmission of respiratory viruses in both community and healthcare settings.
- It is important to use a combination of interventions to achieve the greatest impact.
Proper ventilation is an essential preventive measure to reduce COVID-19 transmission indoors, and the required ventilation rate depends on the type of activity, with mechanical or natural ventilation, recirculation, and intermittent exhaust as options to achieve adequate ventilation volume.
Key points
- Improving ventilation is an important measure to reduce COVID-19 transmission.
- Mechanical or natural ventilation, recirculation, and intermittent exhaust are effective ways to improve ventilation.
- Portable HEPA filters and ceiling-mounted HEPA-UV air filters are recommended for recirculation.
- The minimum efficiency reporting value (MERV) of the filtration system should be targeted to 13 or more.
- The Wells-Riley model can be used to estimate the maximum number of occupants or the maximum residence time allowed in a specific indoor space in advance.
- Administrative controls can be used to limit the number of occupants or residence time when it is entirely impossible to improve the ventilation of the indoor space with engineering controls.
This systematic review examines the effectiveness of ultraviolet germicidal irradiation (UVGI), a feature that can be incorporated into heating, ventilation, and air conditioning (HVAC) systems, in reducing virus transmission. The research found that UV radiation is effective in inactivating viruses and reducing disease transmission; however, practical implementation of UVGI in HVAC systems needs to consider airflow patterns, air changes per hour, and device location. Further field studies could provide important information on system performance in real-world situations, particularly in the context of the current COVID-19 pandemic.
Key points
- Ultraviolet radiation can be effective in reducing the transmission of viruses in indoor spaces.
- Upper-room UVGI disinfection systems can be optimized for ventilated rooms.
- UV radiation can destroy influenza virus suspended in air.
- UV air sterilization can reduce the incidence of respiratory infections in children’s institutions.
- UV irradiation of classrooms can reduce the spread of measles, mumps, and chickenpox.
Ventilation and Coronavirus (COVID-19) (opens in a new tab)
Proper ventilation with outside air can help reduce the concentration of airborne contaminants, including viruses, indoors, but it should be used in combination with other best practices recommended by the CDC to protect people from COVID-19.
Key points
- Increasing ventilation can help reduce the concentration of airborne contaminants, including viruses, indoors.
- Proper ventilation also reduces surface contamination by removing some virus particles before they can fall out of the air and land on surfaces.
- When used along with other best practices recommended by the Centers for Disease Control and Prevention (CDC) and others, increasing ventilation can be part of a plan to protect people indoors.
- Improving ventilation benefits indoor air quality by reducing exposure to products used for cleaning and disinfecting potentially contaminated surfaces.
- Improving ventilation will also help control other airborne infectious diseases.
This article discusses the importance of proper ventilation in indoor spaces to prevent the spread of COVID-19, and analyzes the current regulations and guidelines in Europe and Spain regarding indoor air quality. It concludes that the current criteria established in applicable regulations are insufficient to ensure health and avoid contagion by aerosols indoors.
Key points
- Ventilation is crucial in reducing the risk of COVID-19 transmission in residential buildings.
- Standard ventilation requirements may not be sufficient in the pandemic context.
- Improving ventilation can reduce the concentration of aerosols and other pollutants in indoor air.
- Indoor air quality can have a significant impact on human health and well-being.
- Passive ventilation strategies can be effective in improving indoor air quality.
Ventilation in Buildings (opens in a new tab)
Proper ventilation, including increasing outdoor air delivery, filtration, and air cleaning, can help reduce the concentration of viral particles in indoor spaces and lower the risk of exposure to COVID-19.
Key points
- Indoor air movement and dilution of viral particles through mechanical or nonmechanical means can reduce the airborne viral concentrations and the overall viral exposure to occupants.
- Ventilation system upgrades or improvements can increase the delivery of clean air and dilute potential contaminants.
- Implementing multiple building-level mitigation strategies at the same time is consistent with CDC’s layered approach and will increase overall effectiveness of ventilation interventions.
- Ventilation interventions can reduce the spread of disease, but they will not eliminate risk completely.
- Improving air circulation and cleanliness can help reduce viral particle concentration.
- Aim for 5 or more air changes per hour (ACH) of clean air to help reduce the number of germs in the air.
- The ventilation interventions listed above come with a range of initial costs and operating costs.
Ventilation reduces the risk of COVID. So why are we still ignoring it? (opens in a new tab)
Proper ventilation is a crucial component in reducing the transmission of COVID-19 and other airborne viruses, yet it is often overlooked in control measures, and there needs to be greater awareness and action taken to improve indoor air quality.
Key points
- Ventilation is a key measure to reduce the risk of transmission of COVID-19.
- Ventilation reduces the concentration of airborne virus that can cause infection.
- Vaccines are not effective in preventing transmission.
- Wearing a mask reduces the risk of spreading and acquiring an infection.
- Sufficient and effective ventilation in buildings is necessary to reduce the risk of transmission.
- Ventilation airflow rates must be controlled by the number of occupants in the space and their activity.
- The cost to society of prevention through better designed buildings and gradual improvement of ventilation in existing buildings is much lower than the cost of infections.
- We need a national regulatory group for clean indoor air to establish protection against indoor air hazards in relevant Australian legislation.