There are four exhaust shutter types — gravity (auto-closing), motorised, fixed louvre and external weather hood — and the choice turns on whether the opening must close when the fan stops, how much rain and sand protection you need, and whether you can run a power feed. BAER (Zhejiang BAER Electrical Technology Co., Ltd.), a China exhaust fan manufacturer since 2003 — CE, CB and ISO 9001 certified, MOQ 100 pcs, samples in 3–7 days — supplies shutters matched to every fan it ships.
Gravity, motorised, fixed louvre or weather hood — and why the hinge pins are what actually fail.
Last updated: October 20, 2026
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 |
On panel fans the shutter is built into the housing, so "shutter size" is simply the fan's nominal size — what your installer actually needs to match is the wall cut-out. The KLT series dimensions below are what the mason needs before the fan is ordered:
| Nominal size | Panel (mm) | Wall cut-out (mm) | Airflow | Model |
|---|---|---|---|---|
| 6" | 200 × 200 | 160 × 160 | 150 m³/h (88 CFM) | KLT-10B |
| 8" | 250 × 250 | 205 × 205 | 380 m³/h (224 CFM) | KLT-12B |
| 10" | 310 × 310 | 245 × 245 | 432 m³/h (254 CFM) | KLT-18B |
| 12" | 340 × 340 | 290 × 290 | 792 m³/h (466 CFM) | KLT-20B |
| 14" | 400 × 400 | 330 × 330 | 1,500 m³/h (883 CFM) | KLT-25B |
| 18" | 600 × 600 | 480 × 480 | 1,800 m³/h (1,059 CFM) | KLT-30B |
If the hole is already built, measure it and work backwards — cutting the opening slightly oversize and packing the gap with mortar is normal trade practice; cutting it too small means re-cutting a finished wall.
| 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. And when sizing a new installation, budget the shutter’s drag into your margin with the exhaust fan CFM calculator.
Most wrong-shutter problems are decided before production starts — at the enquiry stage, when one of the fields below is missing. This is the checklist our export team works through for every shutter enquiry:
| Field | Why it changes the answer |
|---|---|
| Wall cut-out or fan size | Fixes the frame size. On the KLT series the shutter is integrated into the housing, so the cut-out matters more than the frame. |
| Wall thickness and facade type | Decides whether an external hood can be fixed, and how far it projects from the wall. |
| Exposure: inland dust, coastal salt or driven rain | Selects the hood and sets the cleaning interval. |
| Closing requirement | Gravity (default) or motorised, where a positive close or a BMS interlock is required. |
| Power available at the fan position | A motorised shutter needs a control feed, not just a supply. |
| Airflow and static pressure | Lets us check the shutter's drag against your sizing margin. |
| Quantity and destination port | Sets the packing and the lead time. |
The shutter is a mechanism, and its service life is set by what gets into the hinge pins. Match the interval to the environment rather than to a fixed calendar:
| Environment | Inspect hinge pins | Clean blades | Replace when |
|---|---|---|---|
| Inland office or residential | Every 6 months | Annually | Blades no longer fall shut on their own |
| Gulf or desert, wind-blown sand | Monthly | Every 3 months | Pins show visible scoring or pitting |
| Commercial kitchen with grease | Monthly | Monthly | Blades feel tacky or stick part-way open |
| Coastal, salt-laden air | Every 2 months | Every 6 months | Corrosion at the pin or the blade edge |
One environment we ship into constantly is the dusty industrial one: a trading partner in Saudi Arabia took 2,000 window-mounted units for factory workshops. In that setting it is dust loading, not shutter design, that sets the cleaning interval — which is exactly why the table above splits by environment rather than by model. The same shutter can be a quarterly job in an office and a much shorter cycle on a workshop floor.
Both the shutter blades and a weather hood sit in the air stream. If you size the fan to exactly the calculated airflow, the airflow actually delivered once the hood and blades are fitted will be lower than the number you sized to. Keep a margin — 10–15% above the calculated requirement is normal practice — and re-check the result with the exhaust fan CFM calculator before the opening size is fixed in the wall.
A shutter specification is only as good as the factory that forms the blades and presses the pins. BAER's manufacturing and export entities are separately registered and documented: Zhejiang Baer Electrical Technology Co., Ltd. holds ISO 9001 (certificate 04625Q15304R1M), and the KLT panel range used in the table above carries CCC certification 2024010702612682. Company registration, certificate scans and the export entity can be checked on our verification page before an order is placed.
Match the shutter to the failure you need to prevent. A gravity auto-shutter suits most wall panel fans where dust and back-draft are the concern; a motorised shutter is for applications that need a guaranteed, powered close; a fixed louvre suits openings where backflow does not matter; and an external weather louvre or hood is added where wind-driven rain hits the facade. The comparison table and the climate recommendations above give the full decision path.
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.
Which shutter to specify depends on what the installation is exposed to: dry inland air is a different problem from coastal salt and monsoon humidity. These pages cover the climate and market context, plus the airflow background behind the choice.
Send your application, quantity and destination — our export team replies within one working day.
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