1. Match the Duct DiameterThe most common mistake is buying a vent that does not fit the duct. Measure your round duct collar: typical sizes are 75 mm, 80 mm, 100 mm (4″), 125 mm (5″), 150 mm (6″) and 200 mm (8″). Bathroom fans usually use 100 mm; kitchen hoods and inline fans often use 125–150 mm.
2. Ceiling vs Wall MountMost round disc valves work on both ceilings and walls, but check the collar depth. Ceiling installations need a flush, low-profile grille; wall installs can use a slightly deeper collar that extends into the duct.
3. Look for an Adjustable DiscA fixed-hole vent cannot balance airflow. Choose a model with an adjustable central disc (butterfly damper) so each room can be tuned on site — this is essential when one fan serves multiple rooms.
4. ABS Plastic Beats Metal in Humid RoomsSteel or aluminum vents look tough, but they sweat and rust in bathrooms. UV-stabilized ABS plastic stays clean, quiet and corrosion-free for years, at a lower cost.
5. Maintenance MattersPick a vent with a removable face grille so you can wipe dust and grease off without tools — especially important in kitchens.
