Designing homes to conserve energy and use it efficiently, from sources that cause least environmental harm.

Active ventilation

Ventilation is required to remove moisture and airborne pollutants from a home to protect the health and comfort of people living there. Ventilation can also be important for temperature control, particularly in summer.

The ventilation rate for houses is often described as the number of air changes per hour (ach). This is how many times a volume of air equal to the house volume has entered and left the house in 1 hour. A healthy ventilation rate is 0.35–0.5 ach. In other words, one third to one half of the volume of air in a house is replaced each hour. Lower than this risks not removing contaminants properly, while higher ventilation rates may require more active space heating.

Houses built in the last few decades of last century typically had infiltration rates around 0.3 ach, with houses built before 1960 having three times this much. These older homes provide the required ventilation just through their ‘air leaky’ construction.

However, houses built after 2000 are typically much more airtight, with closer to 0.2 ach on average.

Building Code requirements

Building Code clause G4 Ventilation requires that spaces within buildings have adequate ventilation for their intended use and occupancy, have adequate fresh air, and have means to remove moisture, products of combustion and other airborne contaminants.

Acceptable Solution G4/AS1 provides means of demonstrating compliance, including – for most buildings – that in occupied spaces the net openable area of windows and other openings must be at least 5% of the floor area. G4/AS1 also provides means of compliance for removing moisture and contaminants from kitchens, bathrooms and laundries, and for using active ventilation.

In most New Zealand homes, passive ventilation (including opening windows) will still be sufficient for most of the year and only localised air extraction systems are needed: range hoods in the kitchen and extractor fans in bathrooms.

However, in some situations, an air supply ventilation system may be necessary where passive ventilation is not sufficient to meet New Zealand Building Code requirements. Multi-unit blocks where some units have only one external wall could be an example. Some air supply ventilation systems use solar or heat recovery technology to provide heating as well as ventilation.

A true heat recovery ventilation system supplies fresh air from outdoors that is warmed by the heat extracted from the air being removed from indoors; it does not simply recycle roof space air.

Heat pumps are sometimes confused with ventilation systems. A split-cycle heat pump is a heating and cooling system. A heat pump does not remove indoor air or bring outdoor air indoors and is therefore not a ventilation system.

More information


Updated: 21 November 2017