How do I properly vent a kitchen range hood through an exterior wall in NB?

A kitchen range hood in New Brunswick must be vented directly to the exterior — never into an attic, soffit, or interior space — using rigid or semi-rigid metal ductwork with a proper wall cap and damper to prevent cold Maritime air from blowing back in. This is one of the most important details in any NB kitchen renovation because our humid summers and cold winters create the perfect conditions for moisture problems if ventilation is done incorrectly.

The basic components of a proper exterior wall venting installation include the range hood unit, rigid metal ductwork (6-inch round or 3.25 x 10-inch rectangular), an exterior wall cap with a gravity damper or spring-loaded damper, and appropriate insulation and sealing around the duct penetration. For most NB kitchens, 6-inch round rigid duct is the standard — it provides better airflow than flexible duct and is far easier to clean. The NB Building Code prohibits using plastic or vinyl duct for range hood exhaust because it cannot handle the heat and grease.

Installation Process

The duct run should be as short and straight as possible — every 90-degree elbow reduces airflow by the equivalent of 5 to 10 feet of straight duct. Ideally, the hood is on an exterior wall and the duct goes straight through. If your range is on an interior wall or island, you'll need to run duct through the ceiling and out a soffit or up through the roof, which is more complex and expensive ($800 to $2,000 more than a direct wall run). A standard through-wall installation runs $400 to $1,200 for the ductwork, wall cap, and labour, on top of the cost of the hood itself ($200 to $1,500 for most residential units).

The exterior wall cap is critical in New Brunswick's climate. Choose a cap with a built-in backdraft damper — this prevents cold winter air from pouring into your kitchen when the hood is off. In areas like Bathurst, Edmundston, and northern NB where winter temperatures regularly drop below -20 degrees Celsius, a spring-loaded damper is better than a gravity flap because wind-driven cold air can push a gravity damper open. Some homeowners add a second inline damper inside the duct for extra protection.

Where the duct passes through the exterior wall, the gap around it must be sealed and insulated. Use fire-rated caulking or expanding foam rated for the application, and ensure the wall's vapour barrier is reconnected around the penetration. In NB's freeze-thaw climate, a poorly sealed duct penetration leads to frost buildup inside the wall cavity, which melts during warm spells and causes hidden water damage and mold growth behind cabinets.

Sizing the hood matters. For a standard 30-inch residential range, you need a minimum of 100 CFM of ventilation, but 300 to 600 CFM is recommended for proper grease and moisture removal. If your hood exceeds 400 CFM, the NB Building Code requires makeup air — a system that brings fresh air into the home to replace what the hood exhausts. This prevents the hood from depressurizing the house, which can cause backdrafting of furnaces, water heaters, and fireplaces — a carbon monoxide hazard.

This is a job for a professional. Cutting through an exterior wall, maintaining the building envelope, and connecting ductwork properly involves carpentry, HVAC knowledge, and sometimes electrical work for the hood's dedicated circuit. A kitchen renovator or HVAC contractor experienced with NB building requirements will ensure the installation meets code and performs properly through our Maritime seasons. Find qualified contractors through the New Brunswick Construction Network to get the job done right.

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Looking for experienced contractors? The New Brunswick Construction Network connects homeowners with qualified professionals:

• Gionetterenovations
• Thirty Four Renovations