Air Is Always Trying to Equalise

Air naturally moves from:

• High pressure to low pressure
• Warm areas to cooler areas
• Inside to outside (and vice versa) when a pathway exists

Your home is constantly interacting with the outdoor environment. Even well-sealed houses experience air movement through doors and windows, exhaust fans, ceiling penetrations, and service penetrations into wall and roof cavities. Air movement is unavoidable — the key is controlling it.

Warm Air Rises, Cool Air Falls

One of the most important principles of air movement is buoyancy:

• Warm air is lighter, so it rises
• Cool air is heavier, so it falls

This is why heat builds up at ceilings, upper levels often feel warmer, and cold air pools in bedrooms, hallways, and lower floors.

If warm air is not actively redistributed, it stays trapped near the ceiling or escapes into the roof space — often wasted.

The Stack Effect: Your Home as a Chimney

The stack effect describes how warm air rises through a building and escapes at high points, drawing cooler air in at lower points.

In winter:

• Warm air rises and leaks out through the ceiling, roof, and upper walls
• This creates negative pressure at lower levels
• Cold outside air is pulled in through gaps, cracks, and floors

This constant vertical air movement helps explain why downstairs rooms feel draughty, bedrooms feel cold even when heating is on, and roof spaces fill with warm air.

Pressure Zones Inside the Home

Different areas of your home sit under different pressure conditions:

• Positive pressure pushes air out
• Negative pressure pulls air in

Every time you turn on a bathroom exhaust fan, rangehood, or clothes dryer, you create negative pressure inside the home. Air must come from somewhere, so it is pulled in through the easiest paths — often from wall cavities, subfloors, or the roof space.

This is why uncontrolled air movement can bring in cold air, moisture, dust, and pollutants.

Why Some Rooms Are Always Cold

Air takes the path of least resistance. Without intentional airflow, warm air stays near the heat source and distant rooms receive very little benefit. Closed doors, long hallways, and isolated layouts all reduce natural heat sharing between rooms.

Simply heating one room does not mean that warmth will spread evenly throughout the home. Without assistance, air stratifies and stagnates.

Moisture Moves With Air

Air doesn’t just carry heat — it carries moisture. When warm, moist air moves into colder rooms and contacts cold surfaces (windows, walls, ceilings), it cools rapidly and releases moisture as condensation.

This is why poor air movement contributes to weeping windows, damp corners, and mould growth behind furniture and in wardrobes. Improving airflow reduces moisture build-up by moving humid air away from cold surfaces and allowing it to be diluted or exhausted.

Modern Homes Change the Rules

Newer homes are better insulated and more airtight than ever before. While this improves energy efficiency, it also means air no longer leaks out naturally, moisture becomes trapped, and pollutants can build up indoors.

In older homes, uncontrolled leakage often masked these issues. In modern homes, designed airflow becomes essential.

Controlling Air Movement Is the Key

Good home performance isn’t about stopping air movement — it’s about directing it. Well-designed systems can move warm air to where it’s needed, remove stale or moist air, maintain more stable pressure, and improve comfort without drafts.

This is where solutions like heat transfer systems, mechanical ventilation, and balanced ventilation come into play — they work with natural air behaviour, not against it.

Why Understanding Airflow Matters

When you understand how air moves in a home, you can:

• Identify why certain rooms are uncomfortable
• Choose the right ventilation or heating solution
• Reduce condensation and mould risk
• Improve indoor air quality
• Lower energy costs

Air movement explains why problems exist — and guides how to fix them properly.