How Much Ventilation Does a House Need?
4-minute read • Updated April 2025
Ventilation is essential for controlling moisture and maintaining healthy indoor air.
But how much ventilation does a house actually need?
Air changes per hour (ACH)
Ventilation is often measured using air changes per hour (ACH). This is the number of times the entire volume of air inside a home is replaced with fresh air in one hour.
For healthy indoor air, a rate of 0.35 to 0.5 ACH is generally recommended. Modern homes built to tighter standards often require mechanical ventilation to achieve this reliably.
Moisture in the home
A typical household produces 8–10 litres of moisture per day from breathing, cooking, showering, and drying clothes. Without enough ventilation, this moisture builds up, leading to condensation, mould, and poor air quality.
The required ventilation rate also depends on the number of occupants, house size, and how much moisture is generated. ASHRAE 62.2 – the international standard for residential ventilation – recommends a minimum of 10 litres per second per room (approximately 36 m³/h per room) to manage moisture and pollutants.
Why modern homes need ventilation
Older New Zealand homes were often leaky enough to allow natural airflow. But modern insulation and double glazing make homes more airtight – great for energy efficiency, but they also trap moisture, CO₂, and indoor pollutants.
This is why modern homes need a properly designed mechanical ventilation system to maintain healthy air quality without losing heat.