What are the NB building code requirements for kitchen ventilation?

The NB Building Code requires exhaust ventilation in kitchens, and best practice in New Brunswick's Maritime climate is a range hood that vents directly to the exterior rather than a recirculating unit. Proper kitchen ventilation is especially important in NB because our high summer humidity combined with cooking moisture creates ideal conditions for mold growth in wall cavities and behind cabinets.

The code requires kitchen exhaust ventilation capable of removing cooking byproducts — grease, moisture, smoke, and odours — from the space. For residential kitchens, a range hood rated at a minimum of 100 CFM (cubic feet per minute) meets the baseline requirement, but most kitchen professionals in New Brunswick recommend 300 to 600 CFM for a standard 30-inch residential range. The general rule is 100 CFM per linear foot of range width, so a 30-inch range calls for at least 250 CFM, and a 36-inch professional-style range needs 300 CFM or more.

Exterior venting versus recirculating is the most important ventilation decision for NB homeowners. A recirculating hood passes air through a charcoal filter and returns it to the kitchen — it captures some grease but does nothing to remove moisture. In our Maritime climate, where summer humidity already pushes indoor moisture levels high, a recirculating hood leaves all that cooking steam in your home. This moisture migrates into wall cavities, behind cabinets, and into ceiling spaces where it promotes mold growth. An exterior-vented hood exhausts both grease and moisture completely out of the building through rigid or semi-rigid ductwork to an exterior wall or roof cap.

Makeup Air Requirements

If you install a range hood rated above approximately 400 CFM, the NB Building Code may require a makeup air system to replace the exhausted air. Without makeup air, a powerful range hood can create negative pressure inside the home, which backdrafts combustion appliances (furnace, water heater), pulls cold air through gaps in the building envelope, and makes exterior doors difficult to open. Makeup air systems can be passive (a motorized damper that opens when the hood runs) or active (a powered unit that tempers incoming air). This adds $500 to $2,000 to the installation cost but is essential for safety and comfort, particularly in NB's cold winters when you do not want raw outdoor air flooding the kitchen.

Ductwork specifications matter for performance. Use rigid metal duct (smooth-wall galvanized or stainless) rather than flexible duct, which restricts airflow and collects grease. The duct run should be as short and straight as possible, with a maximum of two 90-degree elbows. Each additional elbow or foot of duct reduces effective CFM. The exterior termination must have a backdraft damper to prevent cold winter air from flowing back into the kitchen when the hood is off — a critical detail in New Brunswick where winter temperatures regularly drop well below minus 20 degrees Celsius.

Installing a new exterior-vented range hood typically costs $800 to $2,500 including the hood unit, ductwork, and exterior cap, depending on the complexity of the duct run and whether you are cutting through an exterior wall or running to the roof. This is professional-level work that involves cutting through the building envelope, properly sealing and insulating the penetration, and ensuring the duct pitch prevents condensation from pooling — all important details in NB's freeze-thaw climate.

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

• Gionetterenovations
• Thirty Four Renovations