Ventilation guidance

Ventilation guidance

A space’s ventilation will be influenced by how it was designed, how it is currently being used, and the outdoor conditions.

Ventilation guidance

A space’s ventilation will be influenced by how it was designed, how it is currently being used, and the outdoor conditions. Good ventilation will provide fresh, clean air while maintaining comfortable temperature and humidity levels for the people in the space.

Good ventilation helps reduce COVID-19 airborne transmission by quickly and consistently removing the old air and replacing it with fresh, clean air.
Indicators that a space may not be well-ventilated include a feeling of stuffiness, lingering smells and elevated CO2 levels created by the people in the room. When this is occurring, schools should also consider increasing the use of other measures such as face coverings and physical distancing.

You can quickly improve the air quality in any space by:

  • limiting more vigorous activities, or moving them outdoors or to a better ventilated space
  • limiting the number of people, especially in smaller, confined spaces
  • fully opening all windows and doors to flush the air in the room, and where it’s an option to do so, briefly vacating the room at the same time.

Guidance for all naturally ventilated spaces

Most New Zealand schools and classrooms are naturally ventilated using windows that can be opened. Make the most of this by:

  • Opening all windows and doors as much as possible, and whenever it is practical to do so. Do not wait for a space to get stuffy before opening windows and doors.
  • Opening all windows before the school day starts and having them open whenever the room is vacated during the day.
  • Opening windows and doors on the opposite sides of a room where possible to enable the cross flow of air, including any that connect to internal corridors or other circulation spaces.
  • Taking regular short breaks (5-10 minutes each hour) where everyone exits the space with the windows and doors fully opened, to flush the space with fresh air.

Regularly check for any property issues that may need to be resolved, such as:

  • ensuring any window that was originally designed to open, can still open
  • unsticking windows which may have been fixed or painted shut
  • replacing missing or broken window winders, hinges, catches or closers
  • correcting any previous alterations which may be impeding good ventilation

Please contact your Ministry property advisor if you require additional ventilation support to address any property concerns.

Guidance for naturally ventilated spaces on cold, wet or windy days

Bad weather can make it impractical to fully open windows and doors, but on cold days good ventilation can still be achieved with windows partially opened. 

This is because air flow behaves differently at different temperatures – for example, the bigger the temperature difference between outside and inside, the more efficiently fresh outside air is drawn in through open windows.

As a rule of thumb:

  • it’s possible to achieve good ventilation when partially opening all windows by 5cm  
  • fully opening all windows and doors for 3-5 minutes every hour can fully refresh and replace all the air in a classroom 

On colder days, in addition to our general ventilation guidance, try to:

  • Pre-heat spaces before the start of the school day. Having it warm inside improves the draw of fresh air through partially opened windows.
  • Increase indoor heating during the day, if you need to, to offset the impact of having the windows partially open when it’s cold outside.
  • Where high level windows are fitted, open these first and wider than low level windows to reduce cold draughts in the room.
  • Open lots of windows a little, rather than a few windows a lot. Close the door before you begin closing windows, reduce or close any windows directly facing the worst weather conditions (e.g. wind, rain or snow).
  • On a wet day, try to keep wet clothes out of the classroom as bringing them in will make the classroom more difficult to heat.
  • Consider adjusting the classroom layout to move students away from open windows, and other areas that may have cooler air or draughts.
  • Consider relaxing uniform rules/dress codes and allowing warmer clothes to be worn, for people who are more sensitive to colder air and draughts.
  • Continue to use refresh breaks, where all windows and doors are fully opened and preferably everyone exits the room for a few minutes each hour.
  • Fine-tune your approach through the day as the weather changes. Fully opening windows still achieves the best ventilation, so increase your window openings if it warms up outside later in the day or whenever this can be done while maintaining a comfortable indoor temperature.

Continue using your portable CO2 monitors to check if your ventilation is working effectively, in addition to the appropriate use of face coverings, physical distancing, good hygiene and other health measures.

Guidance for ducted, mechanically ventilated spaces

Some schools are fitted with ducted mechanical ventilation systems that automatically source fresh air from the outside while also managing the temperature of the room. These are often referred to as HVAC or air conditioning systems. This doesn’t include heat pumps, because they don’t supply fresh air.

One way to identify if your space has a ducted mechanical ventilation system is to look for vents in the ceiling that bring in fresh air or extract old air.

Where ducted mechanical ventilation systems are fitted, the above advice for naturally ventilated spaces doesn’t apply unless the system has specifically been designed to work in conjunction with windows and doors being open.  If not, windows and doors should remain closed to allow the system to work as designed. 

A well-configured ducted mechanical ventilation system will provide good ventilation while managing indoor temperatures. Make the most of this by: 

  • Ensuring the system is regularly checked, cleaned and maintained by an appropriately skilled technician.
  • Having the system configured to come on at least two hours before and after the school day.
  • Increasing the amount of fresh air brought in by the system and minimising the amount of old air it filters and recirculates.
  • Continuing to use your portable CO2 monitors to check if the system is working effectively.

Configuration and maintenance of ducted ventilation systems should only be done by appropriately skilled technicians. Technical guidance on this topic is available on our resources page.

Guidance for using heat pumps and other heating systems

You can continue to use heat pumps to heat or cool spaces, even when windows and doors are open. 

Heat pumps and most other heating systems only heat or cool recirculated air within the space. They do not bring in fresh air, so to achieve good ventilation they must be used alongside a means of providing fresh air.  

When using heat pumps and other heating systems:

  • pre-heat the space to a comfortable temperature before the school day to improve the draw of fresh air through partially opened windows
  • increase indoor heating or cooling during the day, if you need to, to offset the impact of having the windows open 
  • resetting the temperature of the room to a comfortable level after it has been vacated and aired out, by briefly closing all windows and doors and running the system on its highest setting before re-occupying the room and re-opening windows.

Ahead of the colder months, your heat pump or heating system should be checked and serviced to make sure it is running at its best.

Using a heat pump with windows open will be less efficient and may incur some additional power costs. 

Other supplementary solutions

Portable air cleaners (purifiers)

Air cleaners are a supplementary solution that can reduce COVID-19 airborne transmission by filtering and recirculating the air within a space. They do not replace good ventilation practices in any circumstances, and do not reduce CO2 levels or supply fresh air.

Air cleaners can offer a modest improvement to air quality and can help compensate when air flow is very low, and in spaces that are challenging to ventilate well. Their effectiveness is dependent on being correctly sized for the room, running on a high fan speed, and having a quality HEPA filter. 

All state and state-integrated schools have been offered air cleaners to use at their discretion in spaces that may have a higher risk of airborne transmission such as some staff rooms, music rooms, high-use meeting and break-out rooms. They can also be used in classrooms and other spaces when adverse weather conditions make it less practical to open the windows.

In addition to the 5,000 air cleaners already being distributed from March 2022, in May 2022 the Ministry allocated an additional 7,500 air cleaners for all state and state integrated schools to support them with ventilation this winter.

If after following our guidance and working through ventilation concerns with your Ministry Property Advisor it is determined that an increased use of air cleaners is the appropriate temporary or supplementary solution, additional air cleaners can be made available.

As the Ministry will supply air cleaners to schools where they are required, there should be no need for schools to purchase their own, however some schools may elect to do so at their own cost. These can be purchased at a discounted price directly from the Ministry's supplier, Samsung New Zealand, using the voucher code published in the 24 May School Bulletin or available by contacting

If purchasing brands outside of these arrangements, our panel of experts recommend air cleaners that use H13-14 HEPA filters, have a Clean Air Delivery Rate (CADR) greater than 400 m3/hour, operate at less than 60dB and do not use emerging technologies that emit any substances into the air (for example ionisers, plasma discharge, ozone generators, photocatalytic oxidation or  hydrogen peroxide).

Ceiling fans

You can use ceiling fans to help circulate warm or cool air around the room. Though they can improve ventilation when windows are fully open, they are unlikely to improve ventilation while windows are partially opened.

Extract and supply fans

Well-designed and positioned extract and supply fans that bring in fresh air or push out the existing air can boost natural ventilation in conjunction with, or as an alternative to opening windows and doors.  If you are considering fitting extract or supply fans, please discuss with your Ministry Property Advisor first to ensure that they will improve existing ventilation.

Portable fans

We recommend limiting use of portable fans as it can be difficult to determine whether they are assisting or interfering with air flow. Portable fans are also noisy and can be a safety hazard depending on how they are positioned in the room. 

Most non-industrial portable fans do not produce sufficient air movement to offer a notable improvement to ventilation.