How do I size a hood CFM for my NB kitchen?

Match your hood's CFM rating to your cooking style and range output — for most NB kitchens, 400–600 CFM handles a standard 30" range, while high-BTU gas ranges need 600–1,200 CFM.

Getting the CFM (cubic feet per minute) right matters more in New Brunswick than in many other provinces. Our Maritime summers bring high humidity into the kitchen, and our winters trap cooking moisture inside tightly sealed homes — an undersized hood leaves grease, steam, and odours recirculating through your space.

The Basic Sizing Rules

The most reliable starting point is your range's BTU output. For gas ranges, divide total BTU by 100 to get your minimum CFM. A standard 4-burner gas range at 40,000 BTU needs at least 400 CFM. A high-output range (60,000–80,000 BTU) needs 600–800 CFM minimum. For electric ranges, the rule of thumb is 100 CFM per linear foot of range width — a 30" electric range needs roughly 250–300 CFM, though 400 CFM gives you comfortable headroom.

Hood placement also affects sizing. Wall-mount hoods positioned 24–30" above the cooktop perform as rated. If your hood sits higher (36"+ above the range, common in open-concept kitchens with tall ceilings), add 25–50% more CFM to compensate for the extra capture distance. Island hoods need 25% more CFM than wall hoods of the same width because they lack a wall to help contain rising air.

Duct Size and Static Pressure

CFM means nothing if your ductwork can't move the air. A 400 CFM hood needs a minimum 6" round duct (or equivalent rectangular). A 600+ CFM hood needs 7"–8" round. Undersized ductwork creates back-pressure, makes the hood noisy, and dramatically reduces actual airflow — a common installation mistake in NB renovations. Keep duct runs as short and straight as possible; every 90-degree elbow costs you roughly 10% of effective CFM.

NB-Specific Considerations

In New Brunswick, all range hoods must vent to the exterior — recirculating hoods with charcoal filters are not an acceptable substitute for a kitchen that sees regular cooking. NB's humid summers mean recirculated air just redistributes moisture and grease back into the kitchen. This is especially important in older NB homes (1960s–1990s) where kitchens were often designed without proper exterior venting — you may need to run new ductwork through a wall or ceiling, which adds $300–$800 to the project.

If your hood exceeds 400 CFM, the NB Building Code requires makeup air — a fresh air intake to replace what the hood exhausts. Without it, a powerful hood creates negative pressure, backdrafting combustion appliances (gas furnaces, water heaters) and making doors hard to open. This is a code requirement, not optional.

Practical Tips

Start by checking your range's BTU rating on the spec sheet or manufacturer's website. Then measure your duct run from the hood to the exterior — shorter is always better. If you're replacing an existing hood, check the duct diameter before buying; upsizing the duct may be necessary if you're moving to a more powerful unit. Noise level (measured in sones) matters too — a 600 CFM hood rated at 4–6 sones is noticeably quieter than a budget unit at 8–10 sones.

Hire a professional for the ductwork and any electrical connections. Hood installation itself is manageable for a confident DIYer, but cutting through exterior walls, adding makeup air intakes, and ensuring proper backdraft dampers are installed correctly is work worth leaving to a licensed contractor.

Need help finding a kitchen renovator who can assess your ventilation setup? New Brunswick Kitchens can match you with a local contractor for free.