A range hood that looks powerful and one that actually clears smoke and grease are often two different appliances, and the number that separates them is range hood CFM. CFM, or cubic feet per minute, measures how much air the hood moves, and getting it right means the difference between a kitchen that stays fresh and one where the smoke alarm becomes your cooking timer. Undersize it and searing a steak fills the house with haze; wildly oversize it and you create backdraft and makeup-air problems. Here’s how to land on the correct number for your kitchen.
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How to Calculate the Range Hood CFM You Need
The right range hood CFM depends primarily on your cooktop’s heat output and the hood’s width, and the calculation differs for gas versus electric. For electric ranges, a common rule is 10 CFM per linear inch of cooktop width, so a 30-inch range wants at least 300 CFM. For gas, sizing follows BTU output: total your burners’ BTU rating and divide by 100. A gas range with four burners totaling 40,000 BTU therefore needs roughly 400 CFM. Powerful pro-style gas ranges pushing 60,000 to 90,000 BTU can demand 600 to 900 CFM or more.
Gas Versus Electric Sizing
The fuel type drives very different requirements, and this is where many homeowners guess wrong.
- Electric cooktop: 10 CFM per inch of width; 30-inch = 300 CFM, 36-inch = 360 CFM.
- Standard gas range: Total BTU divided by 100; typical 400 to 600 CFM.
- Pro-style gas (high BTU): 600 to 1,200 CFM, often requiring makeup air.
- Induction: Similar to electric, though less radiant heat means the number can trend to the lower end.
Always size to the higher of the two methods if your situation straddles them, and add capacity if you cook heavily, wok-fry, or do a lot of high-heat searing that generates smoke and grease-laden vapor.
Don’t Forget Duct Size and Length
All the CFM in the world is wasted if the ductwork chokes it. Every foot of duct, and especially every elbow, adds static pressure that reduces effective airflow. A 400 CFM hood ideally uses 6-inch round duct; jump to 600 CFM or higher and you want 8-inch or even 10-inch duct. Rigid metal duct outperforms flexible, and smooth interiors move air far better than ribbed flex hose. Keep the run as short and straight as possible, since each 90-degree elbow can cost the equivalent of several feet of straight duct. Vent to the outdoors, never into an attic or crawl space where grease and moisture accumulate.
Ducted Versus Ductless Hoods
A ducted hood exhausts air and everything in it to the outside, which is always the better performer. A ductless, or recirculating, hood pulls air through a charcoal filter and blows it back into the kitchen; it captures some grease and odor but does nothing for heat and humidity, and the CFM ratings are effectively lower because the filter resists airflow. Choose ductless only when running a duct is truly impossible, such as an interior island in a condo. If you must recirculate, replace the charcoal filters every three to six months or the hood becomes little more than a noisy fan.
The Makeup Air Requirement
Here’s the detail that catches high-power installs: exhausting a lot of air means a lot of air has to come back in. Many building codes require a dedicated makeup air system for any hood rated above 400 CFM, because a strong hood in a tight, well-sealed modern home can create negative pressure that backdrafts a water heater or furnace flue, pulling dangerous combustion gases into the house. A makeup air kit brings in fresh outdoor air, often tempered, to balance the exhaust. If you’re installing a 600-plus CFM hood, budget $500 to $2,000 for makeup air and confirm your local code, because inspectors are increasingly strict on this.
Noise, Sones, and Variable Speed
A hood you won’t run because it’s too loud protects nobody. Noise is measured in sones, and lower is quieter; 1 sone is barely audible, while a cheap hood at full blast can hit 7 or 8 sones. Look for a hood rated around 1 to 3 sones on its lower speeds. This is why buying more CFM than you usually need can be smart: a 600 CFM hood run at half speed clears everyday cooking quietly and gives you full power in reserve for the smoky nights. Multi-speed and boost functions let you match airflow to the task instead of living at maximum noise.
Putting It All Together
Start with the correct CFM for your cooktop, then verify your ducting can actually deliver it and check whether makeup air is required. A 30-inch electric range in an open kitchen is well served by a quiet 300 to 400 CFM ducted hood on 6-inch rigid duct. A 36-inch gas range calls for 500 to 600 CFM and thoughtful ductwork, and a pro range pushes you into makeup-air territory. Mount the hood 24 to 30 inches above an electric cooktop and 30 to 36 inches above gas, size it at least as wide as the range, and you’ll have a kitchen that clears the air as fast as you can fill it.
Hood Styles and How Capture Area Affects Performance
CFM gets all the attention, but the hood’s shape and capture area matter just as much for real-world results. A wall-mount chimney hood and an under-cabinet hood both sit against a wall with two walls of the cooktop already contained, so they capture smoke efficiently at a given CFM. An island hood, hanging over a cooktop open on all four sides, has to fight cross-drafts and rising plumes with no walls to help, so it generally needs 15 to 30 percent more CFM than a comparable wall hood to do the same job. Downdraft systems, which pull air down and out from behind or beside the cooktop, fight physics the hardest since heat and smoke rise, and they typically need the highest CFM of all while still underperforming an overhead hood.
Sizing the hood wider than the cooktop dramatically improves capture. A hood that overhangs the cooking surface by 3 inches on each side catches the plume before it escapes the edges, which is why a 36-inch hood over a 30-inch range outperforms a 30-inch hood at the same CFM. The depth and shape of the canopy help too; a deeper canopy and a well-designed grease baffle create a larger capture volume that holds the rising smoke long enough for the fan to pull it out.
Filters, cleaning, and long-term performance
A hood only moves its rated CFM when the filters are clean, and this is where neglected hoods quietly fail. Baffle filters, the overlapping metal channels found on better and pro-style hoods, capture grease efficiently and are dishwasher-safe, making them easy to keep clear. Mesh filters trap grease too but clog faster and need washing every couple of weeks under heavy cooking. Charcoal filters on ductless hoods don’t wash; they get replaced every three to six months, and a saturated one chokes airflow to a fraction of the rating.
Set a cleaning rhythm based on how you cook. Degrease baffle or mesh filters monthly for average use, more often if you fry or wok-cook, running them through a hot dishwasher cycle or soaking in hot water with a degreaser. Wipe the hood interior and the fan housing periodically, since baked-on grease is both a performance killer and a genuine fire hazard directly above open flames. A well-maintained hood keeps delivering its rated airflow for a decade or more, while a grease-clogged one becomes little more than an expensive light fixture that hums.
Mounting height, ducting shortcuts, and final checks
Even a perfectly sized hood underperforms if it’s hung wrong. Mount an under-cabinet or wall hood 24 to 30 inches above an electric cooktop and 30 to 36 inches above gas, splitting the difference toward the lower end for shorter cooks so the canopy sits where the plume actually rises. Too high and the smoke disperses before it’s captured; too low and you risk heat damage and headroom problems. For a downdraft, remember it fights rising heat, so it needs the highest CFM and still struggles with tall stockpots.
The most common ducting mistakes quietly rob a hood of half its rated airflow. Crushing flexible duct behind a cabinet, using undersized 4-inch duct on a 400-plus CFM hood, stacking multiple sharp elbows, and reducing the duct diameter at the wall cap all choke the system. Keep the run short and straight, use smooth rigid metal, size the duct to the hood’s outlet, and choose an exterior wall or roof cap with a large free-air opening and a damper that actually opens under airflow. Before you finalize any purchase, verify three things together: the CFM matches your cooktop’s heat output, your duct path can deliver that airflow, and whether a makeup air system is required above 400 CFM in your jurisdiction. Nail those and the hood will pull smoke, grease, and steam out of the kitchen as reliably as the day it was installed.
