Home ventilation

Cold, damp homes with mould and mildew are common in New Zealand – and poor ventilation is a big part of the problem. Proper ventilation can help make your home warmer, dryer and healthier. 

How it works

Did you know that, according to Smarter Homes, cooking creates around 3 litres of moisture every day in the average kiwi home? And every time you take a shower, you create another 1.5 litres. Drying washing, doing dishes, even breathing – they all create moisture. Moisture can also get in from damp ground underneath your home. That’s why ventilation is so important – because unless you get rid of that moisture, it can do a lot of damage. 

Excess moisture makes homes colder because it’s harder to heat damp air. It encourages mould and fungi which are bad for our health, and can damage your clothes, your belongings, and your house itself.

There are a number of ways to ventilate your home. They range from simply opening your windows, to installing extractor fans in high moisture areas, up to home ventilation systems for your whole house.


Research from BRANZ found that opening windows fully for 10-15 minutes can provide sufficient ventilation to replace most of the moist air inside a room. It also showed that most of the heat in the walls and furniture was retained – and rooms with dryer air are easier to heat. Getting into a habit of opening windows for 15 minutes in the mornings can make a big difference.

Extractor fans

In high-moisture areas like kitchens and bathrooms, windows typically don’t provide enough ventilation on their own. That’s why the healthy homes standards specify extractor fans should be installed in these areas. 

Extractor fans remove or ‘extract’ moist air from your home to the outside. Depending on where they’re installed, they can vent to the outside directly through an external wall or window, or via ducting.

Home ventilation systems

Home ventilation systems which are sometimes also known as continuous mechanical ventilation systems, provide an automated ventilation system for your whole house. There are three main types of home ventilation system. The best type for you will depend on the type, age and condition of your home.

  • Positive pressure systems: These bring fresh air in from outside through one or more vents and circulate it throughout the house, which then forces stale, moist air out through gaps and cracks around doors and windows. That’s why they can be a good solution for older homes which tend to have more gaps and places where stale air can escape. Note: some positive pressure systems circulate air from roof cavities, rather than fresh air from outside. However, the air in roof cavities can often be low quality due to pollutants. It’s important you discuss your options with your ventilation provider to ensure they are suitable and refer to the Healthy Homes Standard and building code for more information.
  • Negative pressure systems: Continuous, extract only supplemented by window vents may be a cost-effective retrofit option for many homes.
  • Balanced or neutral pressure systems: These tend to be used in newer homes and apartments that are more airtight. Like positive pressure systems they bring fresh air in from the outside which is ducted throughout your home, but they also extract stale air to the outside at the same time – so there’s a constant balance of fresh air coming in and moist air going out. Many feature a heat recovery system where outgoing stale air preheats the cooler incoming fresh air (in winter, and the opposite in summer), making heating and air conditioning more efficient.

Moisture barriers

Another way of reducing moisture in your home is to stop it getting in in the first place. Insulation can help. So can installing a moisture barrier – something as simple as a sheet of heavy polythene under the house. 

Learn more about ventilation and reducing damp in your home

How much it costs

The costs below are approximate and have been sourced from New Zealand Green Building Council

  • Extractor fans: Around $1,000 installed on average.
  • Home ventilation systems: From around $15,000-20,000 installed for an average home including heat recovery.
  • Moisture barriers: From around $7 per square meter installed.

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Extractor fans

You’ll need to periodically clean the grills, filters and extractor fan unit to keep them free of dust, dirt and grease but ensure it’s unplugged from the power source. 

If there is ducting, you’ll also need to check periodically for holes or gaps, and replace if necessary.  

(Source: The Heating Company)

Home ventilation systems

To keep your system operating properly and extend its life you’ll need to regularly:

  • clean the filters and replace as needed – around every 12 months;
  • ensure vents, grills and fans are free of dust and dirt;
  • check condensate drains for blockages;
  • check the ducts for damage;
  • have the system serviced periodically by a qualified installer.

(Source: level.org.nz)

Benefits — for you and the planet

Better air quality

Ventilation helps remove airborne pollutants from inside your house, which means you’re breathing better quality air.

Is it right for you? 

Ensuring your home has adequate ventilation is important for everyone. If you don’t already have extractor fans fitted in bathrooms and kitchens, remember that they’re a requirement for New Zealand’s healthy homes standards.

Home ventilation systems can be a good whole of house option if ventilation is an issue. But you may want to consider whether your insulation and/or heating is up to scratch first.  They all work together to help create warm, dry and healthy homes. 

Other things to think about

Extractor fans

According to Tenancy Services, if you’re installing an extractor fan, the fan and ducting should be at least 150mm in diameter for kitchens and 120mm for bathrooms. You should also check the exhaust capacity so ask your supplier if you’re not sure. The healthy homes standards have minimum requirements for new homes of at least 50 litres per second for kitchen extractor fans, and 25 litres per second for bathroom extractor fans.

Home ventilation systems

Some positive pressure home ventilation systems recycle air from your roof cavity, rather than bringing in fresh air from outside. However, the air in roof cavities can often be low quality due to pollutants. It’s important you discuss your options with your ventilation provider to ensure they are suitable and refer to the Healthy Homes Standard and building code for more information. 

How to get adequate ventilation for your home


HomeFit self-assessment is a straightforward way to check if a home is warm, dry, efficient and safe. You can use it to check a home you’re looking to buy or rent, or if you want to know how you can improve your current home. It starts with a simple online check.

If you would prefer to speak to someone you can contact an independent HomeFit assessor who can visit your home to provide a detailed assessment and list of priorities. 

HomeFit was developed by the New Zealand Green Building Council and is proudly supported by ANZ.

Important information

The material is information only and you should seek professional advice about your circumstances. While we’ve taken care to ensure the information is reliable, we don’t warrant its accuracy, completeness, or suitability for your intended use. To the extent the law allows, we don’t accept any responsibility or liability arising from your use or reliance on this information.