How Much Ventilation Does a House Need?
4-minute read • Updated April 2025
Quick Answer
A house needs enough ventilation to remove moisture, pollutants and stale air while supplying suitable outdoor air. The required airflow depends on the home's size, occupancy, moisture generation, airtightness and the ventilation strategy — so one airflow number does not fit every house.
Key Terms
Airflow: The volume of air moved through a space over time, commonly expressed in litres per second or cubic metres per hour.
Air changes per hour (ACH): The number of times the equivalent volume of air in a room or building would be replaced in one hour at a given airflow.
Moisture load: The amount of water vapour being added to a home by people and activities such as showering, cooking and drying clothes.
New Zealand Home Example
A small home occupied by several people can have a higher moisture load per cubic metre than a larger lightly occupied home. Ventilation design therefore needs to consider both building size and how the occupants use it.
EVOAQ Answer
EVOAQ designs ventilation around airflow requirements, room use and moisture sources rather than applying one arbitrary whole-house number.
At a Glance
| Factor | Why it matters |
|---|---|
| Occupancy | People add moisture and CO₂ continuously |
| Home size | Changes the volume of air being managed |
| Moisture sources | Showers, cooking and drying clothes can create high local loads |
| Airtightness | Changes how much uncontrolled air enters and leaves |
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.