How Backdraft Dampers Protect Your Home
A range hood exhaust line is a direct 6-inch to 8-inch hole through your building's exterior thermal envelope. To prevent outside rain, insects, rodents, and freezing outdoor air from pouring into your home, the system relies on one-way mechanical check valves called backdraft dampers.
A properly installed system has two dampers: an internal damper located right at the range hood exhaust collar, and a secondary spring-loaded or gravity flapper inside the exterior wall hood cap on your outer siding.
1. The Grease-Glued Damper Flap
Over several years, grease vapor coats the light aluminum flapper door and its steel pivot hinge pins. Once the grease cools, it turns into sticky amber resin.
The damper flap gets glued in one of two positions:
- Glued Closed: When you turn the fan on high, the weak blower cannot push the sticky door open. Exhaust air hits a brick wall and recirculates out the hood sides, filling your kitchen with smoke.
- Glued Open: The door stays permanently cocked open by 45 degrees. Freezing winter wind blows directly down the duct into your kitchen, causing massive heat loss and icy stovetop metal.
2. The Annoying "Wind Clacking" Noise
On homes in exposed coastal areas like Oak Bay, Fairfield, Cadboro Bay, and Sidney, ocean wind creates negative pressure differentials across siding. Cheap unweighted sheet-metal flappers flap open and slam shut against the metal wall cap every two seconds: CLACK... CLACK... CLACK...
The Permanent Acoustic Fix:
- Inspect the exterior wall cap from an extension ladder or balcony.
- Clean all gummy grease residue from the hinge pins with mineral spirits.
- Install a strip of closed-cell neoprene foam weatherstripping tape along the rim where the metal flap makes contact with the metal housing. This cushions the impact, making the door 100% silent during heavy windstorms.
- Ensure the light counterweight spring has not snapped or rusted away in the marine salt air.
Professional Kitchen Ventilation Service in Victoria
West Coast Wrench inspects exterior wall caps, replaces damaged backdraft dampers, and acoustically seals noisy range hood ducting across Greater Victoria, Saanich, Langford, and Sidney.