Last updated: September 10, 2026
Cut-out sizes, mounting position, wiring practice, sealing and the commissioning checks that catch a failed install.
A panel exhaust fan is a two-hour job for someone who has done it before and a two-day job for someone who has not. This guide covers the five decisions that determine whether the installation works: where to cut, how high to mount, how to wire it, how to seal it, and what to check before you sign it off.
Electrical work must be carried out by a qualified electrician and must comply with the wiring regulations of the country of installation. The guidance below is for planning and specification purposes. It is not a substitute for local code or for a licensed installer.
The panel is larger than the hole. Use the install size below, not the panel size — a common error that leaves a fan that does not cover the opening.
| Model | Panel size | Wall cut-out | Duct / outlet |
|---|---|---|---|
| KLT-10B 6-inch | 200×200 mm | 160×160 mm | Φ85 |
| KLT-12B 8-inch | 250×250 mm | 205×205 mm | Φ100 |
| KLT-16B 9-inch | 280×280 mm | 225×225 mm | Φ100 |
| KLT-18B 10-inch | 310×310 mm | 245×245 mm | Φ100 |
| KLT-20B 12-inch | 340×340 mm | 290×290 mm | Φ100 |
| KLT-25B 14-inch | 400×400 mm | 330×330 mm | Φ150 |
| KLT-30B 18-inch | 600×600 mm | 480×480 mm | Φ150 |
Cut the opening 3–5 mm larger than the stated figure so the fan body drops in without forcing. Check the squareness of the cut with a diagonal measurement — an out-of-square hole shows as a visible gap at one corner of the panel.
Position matters more than height. The fan should pull air across the room, not short-circuit from the nearest opening to the nearest exit.
| Symptom | Most likely cause | Check |
|---|---|---|
| Fan does not start | No supply, or a tripped protective device | Prove the supply at the fan terminals; check the spur and the breaker |
| Airflow feels weak | Shutter stuck, duct disconnected, or the room is starved of make-up air | Shutter travel, duct connection, and whether air can enter the room |
| Loud humming, little air | Reversed rotation | Correct the wiring to the motor |
| Rattling | Loose panel fixing or a foreign object in the impeller | Isolate the supply before opening the grille |
| Shutter stays open | Dust or grease on the hinge pins | Clean the pins; add a cleaning interval to the maintenance schedule |
| Trips on start-up | Incorrect supply frequency or a motor fault | Confirm the nameplate frequency against the site supply |
Use the fan's install size, not its panel size. For the KLT series the wall cut-out ranges from 160 by 160 mm on the 6-inch KLT-10B to 480 by 480 mm on the 18-inch KLT-30B. Cut 3 to 5 mm oversize so the body drops in without forcing.
High on the wall, diagonally opposite the main air entry so air sweeps across the room. In a bathroom, mount opposite the door rather than directly over the shower, and avoid mounting right beside a window or door that is normally open.
The cutting, fixing and sealing are within reach of a competent DIY installer, but the electrical connection must be made by a qualified electrician and must comply with local wiring regulations. The fan must be earthed and needs a local means of isolation.
It needs a means of local isolation such as a fused spur, and it should be protected to suit the cable and the installation position. Whether it shares a circuit or has a dedicated one depends on local regulation and on whether the fan has a timer or sensor.
The four usual causes are a stuck auto-shutter, a duct that has come off its spigot, a room with no path for make-up air to enter, and reversed rotation. Check those four before assuming the fan itself is faulty.
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