What It Is

A trickle vent is a small, built-in slot or grille, usually located at the top of a window or door frame, that allows a controlled flow of fresh air into a room even when the window is closed and locked. It typically features a sliding or flap mechanism that can be manually opened or closed, though it is designed to remain open most of the time for continuous ventilation.

How It Works

The vent works passively, using the natural pressure difference between the inside and outside of the building, caused by wind and the stack effect (warm air rising inside the building). This allows stale, humid air to escape while fresh, drier air enters, providing a small but consistent airflow—usually around 5–10 litres per second per vent. This background ventilation helps regulate humidity, reduce condensation, and prevent mould growth without the heat loss associated with fully opening a window.

Benefits

Prevents condensation and mould by continuously removing moisture-laden air,
Maintains indoor air quality by allowing pollutants and CO2 to escape.
Energy-efficient because it provides ventilation without significant heat loss.
Discreet and unobtrusive, blending into modern window designs.