COVID-19 - Masks & Ventilation

COVID-19 - Masks & Ventilation

COVID-19 is airborne and can spread easily from one person to another. There are some key things you can do to minimise the risk of infecting others, including wearing masks and ventilating spaces, such as opening windows.


Why ventilation and masks are important

Artwork of children in class in masks by Dalveena Kaur

Opening windows and doors combined with mask wearing reduces the risk of COVID-19 spreading. That’s because if someone is sick with COVID-19 then the virus is more likely to spread and infect others if windows and doors are closed.

It’s important to open windows and doors so fresh air from outside can move inside, which helps lower the risk of someone catching COVID-19.

NIWA Taihoro Nukurangi air quality scientists have made a short video using a special camera. The video shows what happens to our breath when we're indoors, with and without masks and with high and low airflow. It shows how mask wearing and ventilation reduces the chance of infecting others.

CO2 sensing camera picks up breath plumes (video from NIWA) 

Read KidsHealth information on COVID-19 - what you need to know

How to help stop COVID-19 spreading

One of the most important things you can do is ventilate the space you are in with natural airflow. COVID-19 particles can hang around in indoor spaces like buses, classrooms and homes for hours. Opening windows and doors to create airflow helps keep you, your whānau and others safe.

How can we improve ventilation?

It’s important to open windows and doors whenever possible, even in winter. Natural ventilation can provide fast, safe protection against COVID-19.

Below are some drawings showing how ventilation can help reduce the spread of airborne viruses like COVID-19.

When all windows and doors are closed, exhaled breath containing carbon dioxide (CO2) and airborne viruses can gather in the air and move around the room.

When the windows/doors are open, a cross-breeze helps push CO2 and viruses outside.

A heat pump does not improve ventilation. It moves the air around inside. Although it makes the air colder or warmer, it does not improve the quality of the air. The risk of breathing in COVID-19 or other viruses does not change.

HEPA filters can be used to improve the quality of the air. These filters take in air and remove virus particles before returning the air to the environment.

Key things to know about improving ventilation

  • open windows and doors whenever possible, especially during sleep times
  • open windows or doors on opposite sides of the room so the air can flow more easily 
  • make sure all windows can be opened safely
  • keep windows open even in winter - opening several windows as little as 5cm creates an effective flow, reducing the risk of infection
  • opening doors and windows fully for as little as 15 minutes exchanges stale air inside for fresh outside air
  • heat pumps do not exchange inside air for fresh outside air, nor remove the virus - if your heat pump is on, make sure you still open windows to improve ventilation
  • HEPA filters can be purchased to improve the quality of the air - these filter the virus and allergens out of the inside air, reducing the risk of infection

Check the Unite Against COVID-19 website for information about ventilation and COVID-19

Nanogirl puts COVID-19 classroom ventilation theories to the test.

Read more about ventilation in schools.

The team at Airtime For Air have some tips on how to help stop COVID-19 spreading - below.

Wearing masks

Wearing a mask and opening windows when travelling in a car, uber or taxi reduces the risk of COVID-19 spreading.

Graphic of bus with text 'COVID blows - vent your ride'

Staying outside

Catching up with family and friends outside when possible helps stop COVID-19 spreading.

Graphic of people outside with the words 'COVID blows - take it outside'


Open windows and doors at home and at work to create airflow.

Graphic of someone inside opening a window with the words 'COVID blows - let it out'

One of the most important things you can do is ventilate the space you are in with natural airflow. COVID-19 particles can hang around in indoor spaces like cars, homes and workplaces for hours.

Graphic of people inside with window open with the words 'COVID blows - let it out'

Personal and shared responsibilities

Many different interventions are needed to help stop COVID-19 from spreading. 

Graphic of the Swiss Cheese COVID-19 Prevention Model

How COVID-19 spreads

COVID-19 spreads between people who are close to each other. It spreads most easily in closed spaces, crowded settings and where there is poor ventilation. The World Health Organisation developed this video to show how the virus is transmitted.

More KidsHealth content on COVID-19

Find out about caring for a child with COVID-19

See KidsHealth's section on COVID-19

See all KidsHealth's content on COVID-19 immunisation in children


Thanks to the team at Airtime for Air for sharing their resources with KidsHealth. Airtime for Air was founded by four New Zealand mums who want to help Kiwis reduce the risk of COVID-19. They include academic health economist Dr Katherine Stevens, lawyer Catherine Poppelwell, graphic designer Emily Wong and marketing communication consultant Lina Montero Soto.  

The images on ventilating spaces were sourced from the Numeroteca website.

Artwork of children in masks in a classroom by Dalveena Kaur, year 6, Newmarket School.

This page last reviewed 13 September 2022.

Call Healthline on 0800 611 116 any time of the day or night for free health advice when you need it