Ventilation Requires Air Movement — Not Just Openings

Ventilation is not defined by having an opening in the building. It requires air movement — stale air being removed and fresh air replacing it.

When you open a window, air will only move if there is:

• A pressure difference between inside and outside
• Wind creating a flow path
• Another opening for air to exit

Without these conditions, the air near the window may change, but the rest of the home often does not.

Air Takes the Path of Least Resistance

Even when windows are open, air does not automatically circulate through the whole house. Air enters and exits through the closest and easiest paths.

This means:

• Rooms away from the window may see little or no air change
• Closed doors block airflow completely
• Moist air can remain trapped in bedrooms, bathrooms, and wardrobes

Opening Windows Is Weather Dependent

Window-based “ventilation” only works when outdoor conditions cooperate. It relies on:

• Wind direction and speed
• Outdoor temperature
• Humidity levels
• Time of day

On still days, cold nights, rainy weather, or during bushfire smoke events, opening windows is uncomfortable or simply not an option.

You Lose Heat (or Cool) Very Quickly

Opening windows creates uncontrolled air exchange. In winter, warm indoor air is rapidly lost and replaced with cold outdoor air. In summer, hot and humid air enters the home.

This leads to:

• Higher heating and cooling costs
• Uneven temperatures
• Reduced comfort

This is why “open the windows” directly conflicts with energy-efficient building design.

Windows Don’t Remove Moisture at the Source

Moisture is generated in specific areas — bathrooms, kitchens, and laundries. Opening a window elsewhere does little to remove moisture where it is produced.

Without active extraction:

• Moist air spreads through the home
• Condensation forms on cold surfaces
• Mould risk increases

It Relies on Human Behaviour

Natural ventilation only works if people:

• Remember to open windows
• Leave them open long enough
• Open the right windows
• Do it at the right time of day

In reality, windows are often left closed for security, noise, weather, or comfort reasons. Ventilation that depends on perfect behaviour is rarely effective.

What Proper Ventilation Looks Like

Proper ventilation is controlled, consistent, and deliberate. It typically includes:

• Continuous or automated airflow
• Extraction of stale and moist air
• Controlled introduction of fresh air
• Air movement through the whole home

Mechanical ventilation systems are designed to provide reliable air exchange regardless of weather, time of day, or occupant behaviour.

Key Takeaway

Opening windows allows fresh air in, but it is not ventilation. It is inconsistent, weather-dependent, and uncontrolled. In modern, airtight homes, relying on open windows is unlikely to prevent condensation, moisture build-up, or poor indoor air quality.

Proper ventilation requires designed airflow — not hope, habit, or good weather.