Ways to reduce the risk of COVID-19 through air ventilation, air conditioning and air cleaning.
Last updated: 14 July 2022
On this page:
- Reducing the risk of COVID-19 through ventilation
- Buildings without heating, ventilating and air conditioning systems
- Buildings with heating, ventilating and air conditioning (HVAC) systems
- Air cleaning technologies
- Read more about improving ventilation
SARS-CoV-2, the virus that causes COVID-19, spreads in particles that escape from an infected person’s mouth or nose through the air.
The risk of becoming infected increases the closer you are to a person and the longer you are close to that person, especially if this contact occurs in poorly ventilated indoor spaces.
Read more about conditions that affect COVID-19 spread.
The risk of infection can be reduced by:
- air ventilation (which exchanges old air for fresh air)
- air cleaning (which removes the virus in the air without changing the air).
The type and amount of ventilation required will vary from one situation to another. For example, the ventilation required to prevent transmission of COVID-19 in hospitals will be different to that required in households.
Good ventilation is particularly important in two main areas, where the risk of transmission of infection is high, or where there are vulnerable people, such as disabled or older people.
In most situations, you should combine these methods with other personal protection methods such as vaccination, physical distancing, and masks. Read more about Protecting yourself and others.
Buildings without ventilation systems can be effectively ventilated by opening windows and using exhaust fans in the kitchen or bathroom.
This method is usually adequate for most residential buildings which usually do not have HVAC systems. For most of New Zealand, even during periods of cold weather, a room can be ventilated by opening windows for a short period of time without the room becoming too cold.
In an average sized room in a house, opening a window for 15 minutes is sufficient to ventilate the room and introduce fresh air, reducing the risk of transmission of SARS-CoV-2. Opening windows on either side of a room is the most efficient method of ventilating a room as this provides the best flow of air through the room. Opening doors between the rooms will also help to ventilate other spaces such as corridors, which may not have windows.
The Ministry of Social Development recommends that indoor temperature is maintained above 18 degrees (more information available here).
Guidelines for ventilation have been published by The Tenancy Services at MBIE. See Ventilation standard - Tenancy Services, Ministry of Business, Innovation and Employment
The Ministry of Health provides guidance for decreasing the risk of infection in a household where somebody has COVID-19 (more information available at COVID-19: Isolating from others).
Most commercial buildings have HVAC systems. These systems can carry out multiple functions including heating or cooling the air, exchanging stale air for fresh air, altering the humidity, and cleaning the air to remove pollutants, pollen, or dust. The removal of fungi, bacteria and viruses requires specialist systems designed for that purpose.
Understand your HVAC system
There are many different types of heating, ventilating and air conditioning (HVAC) systems. It is important to understand that not all heating systems include ventilation, and some will only heat or cool air (and not provide fresh air). For example, most heat pumps are a “split-system”, with a fan unit outdoors and another indoors. These systems heat or cool the air indoors but the inside and outside air do not mix, so they don’t bring fresh air inside.”
Key questions to ask include:
- does the system recycle air, or use fresh air?
- can the ratios of fresh air and recycled air change?
- is there a filter in the system and what type is it?
- what is the maximum feasible air change rate the system can deliver?
Understand the regulations that apply to your situation
HVAC systems are usually used in commercial buildings or hotels, and not in households.
Managing HVAC systems can aid in reducing the risk of airborne diseases travelling within a building.
Read about keeping these systems well maintained and maximised to reduce the risk of airborne pathogens spreading: Controlling the spread of airborne diseases in commercial buildings – Building Performance.
Read more about the about the building code for ventilation applied to new buildings: G4 Building Code for ventilation – Building Performance.
Undertake regular maintenance
To ensure the HVAC system is working according to specifications, maintenance will usually be done by a qualified ventilation engineer to ensure:
- ducting is cleaned
- filters are cleaned or changed regularly
- fans are operating correctly.
HVAC modifications which may reduce COVID-19 risk
There is guidance on how HVAC systems can be modified to decrease the risk of COVID-19 infection from several national and international organisations (note HVAC systems should be modified by a qualified engineer).
The following guidelines to decrease the risk of infection have been suggested by this guidance:
- Increase the volume of fresh air and decrease the use of recycled air.
- HVAC systems with central air filters may be used to remove virus. Guidelines for the type of filter necessary for removing different sized particles are available.
Note: Modifications to an HVAC system should be undertaken by a qualified engineer.
Air cleaning technologies can remove a wide range of pollutants or infectious organisms from the air without exchanging stale air for fresh air. These technologies can be used as part of an HVAC system, in addition to an HVAC system or instead of an HVAC system.
High efficiency particulate air (HEPA) filters
A high efficiency particulate air (HEPA) filter is a pleated mechanical air filter that can theoretically remove 99.97 percent of particles (dust, pollen, mould, bacteria, aerosols with viruses) with a diameter of 0.3 microns.
Particles of greater or smaller diameter are filtered more efficiently than the 99.97 percent rating, meaning that the minimum standard for the filter is the ability to filter 99.97 percent or greater of all particles.
HEPA filters are mostly found in portable and fixed air cleaning units for indoor spaces.
They can be used in public indoor spaces such as:
- medical facilities
- gas stations
- supermarkets, and
- private indoor spaces such private residences.
There are several issues to be considered when using portable HEPA filters such as:
- the size and number of air filters required will depend on the size and layout of the room
- how many people will occupy the room
- the airflow through the room, in particular any areas without air flow
- the acceptable noise for that location (such as a bedroom).
See further information on air purifiers and air cleaners: Reducing the risk of COVID-19 transmission through the use of air purifiers – University of Otago
Ultraviolet-C light (UVC) can inactivate the SARS-CoV-2 virus by damaging the outer protein coat of the virus. This is one of the reasons why being outside decreases the risk of infection.
However, the dose of UVC required to inactivate the virus can also cause damage to a person’s skin or eyes. It is important for the UVC beam to be shielded to prevent direct contact with skin or eyes.
Some systems use both HEPA filters and UV light. These systems from reputable manufacturers are widely considered to be safe and effective. There are a number of other technologies on the market, some of which are safe and others potentially hazardous. If you are considering one of these, we recommend you seek advice or research the safety and efficacy.
Some UVC lamps generate ozone which can cause irritation to the throat and lungs.
UVC can be used for spaces where HEPA filters are not effective. It is most used for ‘upper air UVC’ where the air near the ceiling of a building is exposed UVC.
Read more about the use of UV lights and lamps: UV Lights and Lamps: Ultraviolet-C Radiation, Disinfection, and Coronavirus - U.S. Food & Drug Administration
- Improving ventilation in the workplace – VIC.GOV.AU
- Clean Air in Buildings Challenge – US Environmental Protection Authority
- Community, work and school – Ventilation in Buildings - Centers for Disease Control
- Guidance for COVID-19 - Risk reduction in residential buildings - American Society of Heating, Refrigeration and Air-conditioning Engineers
- Heating, ventilation and air-conditioning systems in the context of COVID-19 - European Centre for Disease Prevention and Control
- Indoor Air Quality Research Centre, New Zealand