Last updated: September 10, 2026
Gravity, motorised, fixed louvre or weather hood — and why the hinge pins are what actually fail.
An exhaust fan is a hole in the building envelope. When it stops, that hole is still there — and what comes through it is dust, sand, insects, rain, noise and the neighbour's cooking. The shutter is the part that closes the hole, and it is the specification most buyers leave blank. This guide covers the four ways the problem is solved and which one suits which climate.
The blades are hinged and held closed by their own weight. When the fan runs, the airflow pushes them open; when it stops, gravity closes them again. No actuator, no wiring, nothing to fail electrically.
The blades are driven open by a small motor or a spring-return actuator, linked to the fan's control circuit. The blades open positively before or as the fan starts and close positively when it stops.
Angled fixed blades, no moving parts. Cheap and robust, but it does not close — it only breaks the line of sight and sheds some rain.
A separate component fitted on the outside face of the wall. It is not an alternative to the fan's shutter — the two are normally used together.
| Type | Closes when off | Stops dust / insects | Rain protection | Powered | Maintenance |
|---|---|---|---|---|---|
| Gravity auto-shutter | Yes | Yes | Partial | No | Clean hinge pins |
| Motorised shutter | Yes, positively | Yes | Partial | Yes | Actuator check |
| Fixed louvre / grille | No | Partial | Slight | No | None |
| External weather hood | No (add-on) | Yes | Yes | No | Clear debris screen |
| Situation | Specification |
|---|---|
| Gulf / desert, exposed facade | Gravity auto-shutter plus an external weather hood. Sand and wind-driven dust make the hood worthwhile. |
| Coastal site, salt air | Auto-shutter with a hood, and a shorter cleaning interval — salt accelerates pin corrosion. |
| European / North American domestic | Gravity auto-shutter. The priority is heat loss and draughts rather than sand. |
| Commercial kitchen with grease | Auto-shutter, cleaned frequently, or a fixed grille with a separate damper if grease build-up is severe. |
| BMS-controlled project | Motorised shutter so the open and closed states can be monitored and interlocked. |
| Continuously running industrial extract | Fixed louvre is acceptable; a shutter adds nothing when the fan never stops. |
Shutters fail open far more often than they fail closed. The cause is almost always contamination on the hinge pins — sand in the Gulf, grease in a kitchen, salt in a coastal installation. The blades then hang slightly open, which produces three symptoms at once: visible dust ingress, a continuous draught, and a measurable loss of airflow because the blades are sitting in the air stream.
The fix is a maintenance interval matched to the environment, not a different shutter. On a dusty site, clean the pins monthly rather than quarterly.
It is a set of hinged blades held closed by their own weight. Airflow from the running fan pushes them open, and gravity closes them when the fan stops. It needs no power and it fails closed, which is why it is the default on wall panel fans.
If the fan discharges through an external wall, yes. Without one the opening stays open when the fan is off, letting in dust, insects, rain and back-draft from neighbouring spaces, and losing heat in colder climates.
Almost always contamination on the hinge pins — sand, dust or kitchen grease. Clean the pins and check that the blades swing freely. A shutter that stays open also reduces airflow, because the blades sit in the air stream.
It handles dust and back-draft, but it is not a rain seal. On an exposed or coastal facade, fit a gravity auto-shutter for daily operation and an external weather hood for wind-driven rain, and expect to clean the hinge pins more often because of salt.
Not usually as a field modification — shutters are designed into the fan housing. If you need a closing blade set, specify it at order stage, or fit a separate back-draft damper in the duct. On the KLT series the auto-shutter is standard on every model.
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