Ventilation
Fresh or filtered air can reduce your risk of catching or spreading illnesses. Opening doors and windows at home is the simplest way of improving ventilation and helps protect you, your whānau and others.
How illnesses can spread
When a person with a viral infection breathes, speaks, coughs or sneezes, they may spread particles containing the virus.
Respiratory illnesses such as COVID-19, flu (influenza) and measles are mostly spread by small viral particles — these can stay in the air for minutes to hours. Good ventilation helps remove them.
You can reduce the risk of spreading some illnesses by improving ventilation (the movement of fresh air in a close space).
Ventilation when you are sick
It is important to keep the air in your room fresh. If you can, open windows on different sides of the room to help airflow.
To stop viral particles spreading within the home, reduce airflow from your room to other parts of your home:
- before opening the door into shared spaces, open your window for at least 5 minutes to freshen the air
- in a shared bathroom or toilet, close the door after you have been in the room and switch on the extractor fan, or open a window.
How to know if you have suitable ventilation
One way to know whether or not an indoor space is well ventilated when it is occupied is to monitor the level of the gas carbon dioxide (CO2).
People breathe out carbon dioxide and, as they do so, the level of carbon dioxide in a room increases. In a poorly ventilated room, carbon dioxide will stay in the room for longer, building up to higher levels.
- A carbon dioxide level below 800ppm (parts per million) indicates a well-ventilated space.
- A carbon dioxide level above 800ppm suggests you may need to bring more fresh, outdoor air into the space.
- A carbon dioxide level above 2000ppm sustained for over 15 minutes suggests a poorly ventilated space, with a much higher risk of spreading airborne infections.
If you have high carbon dioxide levels in your space or cannot measure carbon dioxide levels but are wanting to improve air quality, there are a range of easy and practical steps you can take.
How to improve ventilation at home
We encourage you to let in fresh air every day, including while someone visits your home and after they leave.
Try 1 or more of these ways to remove stale air.
- Open windows or doors on opposite sides of a room to help airflow.
- Open doors between rooms to ventilate hallways and spaces without windows.
- In kitchens, bathrooms, and toilets, switch on the extractor fan or open a window.
- Open higher windows wider than lower windows. This helps reduce draughts.
- If your windows do not open, check if your ventilation system filters (cleans) the air.
When leaving windows or doors open for periods of time, consider the safety of others — especially disabled people, children and pets.
Steamed-up windows can be a sign of low ventilation.
In cold or wet weather
Try 1 or more of these ways to refresh air without letting rooms get chilly or damp.
- Partly open a window for most of the day, for example, a 5cm opening.
- Fully open a window or door for 3 to 5 minutes every hour.
- Open a window whenever you leave the room, closing the door behind you.
You do not have to leave windows or doors open all the time.
In homes with heat pumps or ventilation systems
Heat pumps, air conditioners and ceiling fans do not bring in new fresh air. Instead, they move around air already in a room. You will need to open doors or windows to remove stale air and let in fresh air.
If you have a home ventilation system, check if it recycles air or filters air:
- If it recycles air, you need to open windows or doors to move stale air out and let in fresh air.
- If it filters or cleans air, this helps remove stale air and reduce the risk of virus particles spreading.
In rental properties
Landlords must provide good ventilation. If you live in or own a rental property, check ventilation rules on the Tenancy Services website.
Ventilation on public transport
Virus particles can build up quickly in crowded places such as buses or trains. It helps to sit or stand close to the door as airflow will be better.
Open a window on the bus if you can. Taxis and ride-share services often ask passengers to open windows.
We encourage you to wear a face mask in closed, crowded, and confined places such as public transport.
Air cleaning technologies
A high-efficiency particulate air (HEPA) filter can remove dust, pollen, mould, bacteria and aerosols. They can filter 99.97% of particles. These filters do not replace the other good ventilation habits already described, as they do not supply fresh air or reduce carbon dioxide levels.
You can find HEPA filters in portable and fixed air-cleaning units for indoor spaces.
They are used in public indoor spaces such as:
- medical facilities
- gyms
- restaurants
- schools
- petrol stations
- supermarkets
- private indoor spaces such as homes.
There are several issues to consider when you are using portable HEPA filters such as:
- the size and number of air filters will depend on the size and layout of the room
- how many people will be in the room
- the airflow through the room, in particular, any areas without airflow
- the acceptable noise for that location (such as a bedroom).
Ultraviolet-C light (UVC) can kill the COVID virus by damaging the outer protein shell of the virus. This is why being outside decreases the risk of infection.
The amount of UVC needed to kill the virus can also damage our skin or eyes. You should shield UVC lights to prevent direct contact with skin or eyes.
Some systems use both HEPA filters and UV light. Systems from reputable manufacturers are safe and effective. There are many 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.