4 Inch Draft Blocker Backdraft Damper Duct One-Way Airflow Inline Fan Vent

A 4-inch backdraft damper for ventilation ducts, used to stop air flowing backward when a fan is switched off. The body is galvanized steel and the flap is aluminum. It slides into the duct as far as it goes, and the spring should sit horizontally when the flap is mounted horizontally, which also applies to vertical installs. It is intended for air conditioners, exhaust fans, extractors, range hoods and heating vents in homes, offices and industrial settings. It fits flexible or rigid metal ducting but not plastic duct, since the sizes differ. Dimensions are measured by hand, so allow a small tolerance of a few millimetres.