A range hood is a canopy with a blower in it, hung over the cooktop to catch the rising column of hot air, grease vapor and combustion gas your pans throw off and push it outdoors. Airflow is rated in CFM, cubic feet of air moved per minute. Loudness is rated in sones, a scale built so that 4 sones sounds twice as loud as 2, with 1 sone close to the hum of a quiet refrigerator. Know what you are clearing: frying and searing put fine particles into the room, and a gas burner adds nitrogen dioxide, carbon monoxide and close to a pint of water vapor for every 10,000 BTU it burns, BTU being the unit that burner output is measured in.
Catching the plume
Catching the plume matters more than the fan behind it. Hot air leaves a pan slowly and spreads as it climbs. The canopy has to sit where the plume arrives, not over the burner it left. Cover the full cooktop width, add 3 inches on each side where a wall allows, and take depth as seriously as width: a 19 inch deep hood over a 25 inch deep cooktop leaves the front burners in open air, and those are the ones you fry on. Height settles the rest. Wall and under-cabinet models are usually listed for 24 to 30 inches above the cooking surface and island models for 30 to 36. Extra headroom is extra room for the plume to spread before the hood ever sees it.
Ducted or recirculating
Where the air ends up splits this market cleanly. A ducted hood sends heat, steam, smoke, grease vapor, odor and combustion products out of the building through rigid metal pipe. A recirculating hood, sold as ductless or convertible, pushes that same air through a charcoal filter and hands it back to the room. Charcoal traps some odor and nothing else, so heat, moisture and most fine particles stay with you. Match pipe to blower: roughly 6 inch round up to 400 CFM, 7 or 8 inch to 600, and 8 to 10 inch above that. Corners cost real flow, because one 90 degree elbow in 6 inch pipe behaves like about 15 feet of straight run. Choose smooth rigid duct over corrugated flex, which halves airflow and holds grease.
Size it from your cooking
Size the blower from your cooking, then pick the shape from your kitchen. On electric, start at 100 CFM per foot of cooktop width, so 250 for a 30 inch and 300 for a 36. On gas, allow 1 CFM per 100 BTU of total burner output, putting a 60,000 BTU range near 600. Add half again for an island, which has no walls to help it, and for anyone who sears or stir-fries several nights a week. An Under-Cabinet Range Hood suits a kitchen that already has a cabinet over the range. A Wall-Mount Chimney Hood buys depth by giving that cabinet up. Downdraft Vents answer an island where nothing may hang overhead, a Hood Insert hides the machinery inside custom joinery, and a Microwave Hood Combination trades ventilation for counter space.
Noise comes first
Every gain here sends a bill somewhere. Noise comes first: a hood rated 8 sones on high is why most people cook with the fan off, and an unused 900 CFM machine ventilates worse than a 400 CFM one you can talk over. Conditioned air is next, because 600 CFM empties the air volume of a 1,500 square foot house in about 20 minutes, and heating that much 28 F outside air back up to 68 costs close to 26,000 BTU an hour. Then the legal bill: past roughly 400 CFM many residential codes require powered makeup air, since a fan that strong can depressurize a tight house enough to pull exhaust back down a water heater or fireplace flue. Thresholds vary by country and locality, so check yours.
Read the airflow claim
Read the airflow claim before the metal. A CFM figure certified by an independent ventilation rating program is measured against real duct resistance, usually 0.1 inches of water gauge. In contrast, an uncertified number often comes from a blower in open air and reads 30 to 50 percent high. Prefer baffle filters, the stainless chevron panels that make air turn sharply so grease condenses and drains into a cup, over layered aluminum mesh that clogs sooner. Press a thumb into the canopy, since 20 gauge stainless barely gives. Compare sones at high, not low. If quiet decides it, buy a model that takes an inline or exterior blower, which moves the motor to the attic or the roof and can drop what you hear at the cooktop to 1 to 3 sones.
Grease decides everything
Grease decides how long a hood lasts and whether it ever catches fire, so the filters set the schedule. Wash them every month you fry or sear, because a loaded filter chokes airflow and then becomes fuel for a flare-up on the burner underneath. Twice a year, pull the filters and clean the blower wheel and housing behind them, since a caked wheel goes out of balance, grows loud and moves noticeably less air. Swap charcoal filters every 3 to 6 months on a recirculating install, and take the charcoal out completely if you later connect a duct, because leaving it in strangles a ducted hood. Blowers give 10 to 15 years and usually fail long before the shell does.
Buyer checklist
Before you buy range hoods
A major appliance must fit the space, the utilities and the service network. Running cost and repair access belong in the first comparison.
01
Measure the full installation
Include doors, handles, hoses, vents, clearance, service access and the delivery path, not only the cabinet opening.
02
Confirm every utility
Check voltage, circuit, plug, water, drain, gas and ventilation requirements against the exact model and local rules.
03
Compare ongoing use
Use the local energy or water label and include filters, detergent, bags and other consumables.
04
Check parts and service
Look for local technicians, realistic warranty coverage and the availability and price of common replacement parts.
Measure the cooktop rather than the cabinet. Buy a hood at least as wide as the cooking surface, 3 inches wider on each side against a wall and 6 inches wider on each side over an island. Then measure cooktop depth: a canopy shallower than about 20 inches leaves your front burners, the ones that smoke, outside the capture area.
Set the mounting height from the model's own instructions, then test it with your tallest stockpot in place. Wall and under-cabinet hoods are often listed for 24 to 30 inches above the cooking surface, island hoods for 30 to 36, and a microwave hood combination at about 66 inches from the floor to its top, which leaves 13 to 18 inches above the cooktop. Going below the listed minimum risks heat damage and voids the listing.
Trace the duct route before you choose a blower. Straight up through a cabinet or out the back wall costs least. Count every 90 degree turn as roughly 15 feet of extra pipe and stay inside the maximum equivalent length in the manual. Use 6 inch round to 400 CFM, 7 or 8 inch to 600, and 8 to 10 inch above that. Flat 3.25 by 10 inch duct hidden in a wall cavity flows like 6 inch round at best.
Confirm the power supply. Most hoods want a grounded 120 volt, 15 or 20 amp connection, and big blowers or remote motors often need their own circuit and hard wiring. Any new circuit is licensed work, as is capping or moving a gas line while the range is out.
Settle makeup air before ordering anything above 400 CFM. In a tight house a fan that size can pull exhaust back down a naturally vented flue. Many codes require a powered supply damper interlocked with the hood, often 500 to 2,000 dollars fitted. The trigger point differs by country and city, so ask your building department instead of assuming.
For a ceiling-hung island hood, find the joists first. These units weigh 60 to 120 pounds and need solid blocking, never drywall anchors. Their chimney covers are cut for an 8 foot ceiling. A 9 or 10 foot ceiling needs the extension piece made for that exact model, ordered at the same time.
Care
Caring for range hoods
Wash the grease filters every month you fry or sear, in hot water with dish soap or a degreaser. A clogged filter chokes airflow and becomes fuel itself. That metal is all that stands between a flare-up on the burner and grease inside the duct.
Degrease the blower wheel and the housing behind the filters twice a year. Grease loads the blades unevenly, and an out-of-balance wheel gets loud, vibrates and moves noticeably less air for months before anything actually fails.
Replace the charcoal filter on a recirculating hood every 3 to 6 months. Spent carbon stops holding odor and only adds resistance. If you later run a duct outdoors, take the charcoal out completely, because leaving it in costs roughly a third of the airflow.
Run the fan once a year and watch the outdoor cap. The damper flap should swing fully open and drop shut afterward. Stuck open it lets cold air, insects and nesting birds in; stuck shut it kills extraction while the motor still sounds perfectly healthy.
Switch the fan on a few minutes before high-heat cooking and leave it running 10 minutes afterward. A moving column of air is far easier to catch than a plume you chase. That last stretch clears the steam that fogs cabinet doors.
Wipe the underside, the light lenses and the canopy edges while they are still warm after greasy cooking. Cooled grease hardens into a yellow varnish that needs a solvent rather than a cloth, and on a plaster or timber surround it stains for good.
Questions
Common questions
How many CFM do I need for a 30 inch range?
Start at 250 CFM for an electric 30 inch cooktop, using 100 CFM for each foot of width. For gas, add the burner ratings instead and allow 1 CFM per 100 BTU, so a 45,000 BTU range wants about 450 and a 60,000 BTU one about 600. Add half again if the cooktop sits on an island or you sear most nights.
Is a ductless hood better than nothing?
Slightly. The metal filter catches grease droplets and the charcoal holds back some odor, so your cabinets stay cleaner. Everything else stays in the kitchen: the heat, the steam, the fine particles from frying and, on gas, the nitrogen dioxide and carbon monoxide. Treat recirculation as a rental compromise and open a window while you cook.
How high above the cooktop should a hood go?
Follow the model's instructions, which usually say 24 to 30 inches for a wall or under-cabinet hood, 30 to 36 for an island hood, and about 66 inches from the floor to the top of a microwave hood combination, which leaves 13 to 18 inches over the burners. Mounting low captures better but bakes the hood; mounting high is comfortable and lets the plume spread past the canopy. Above 30 inches, buy extra width and extra airflow.
What duct size can I get away with, and how long a run?
Use smooth rigid metal: 6 inch round up to 400 CFM, 7 or 8 inch to 600, and 8 to 10 inch above that. Keep it short and straight, because one 90 degree elbow in 6 inch pipe costs about the same flow as 15 feet of straight pipe. The manual gives a maximum equivalent length, and passing it makes the rated airflow fiction.
Do I really need makeup air, or is that an upsell?
It is a safety rule, not a sales line. Above roughly 400 CFM a hood can drop house pressure enough to reverse a naturally vented water heater or fireplace and bring carbon monoxide indoors. Many codes require an interlocked powered air supply at that point. The exact threshold varies by country and city, so ask your building department.
Are baffle filters actually better than mesh?
For high-heat cooking, yes. Baffles are stainless panels that force air to turn sharply, so grease condenses on the metal and drains into a cup rather than loading the filter. They survive a dishwasher and usually outlast the blower. Aluminum mesh costs less and catches fine grease well when clean, but it blocks up faster and dulls in dishwasher detergent.
Is a microwave hood combination enough ventilation on its own?
Over an electric cooktop with moderate cooking, it will do. It moves 300 to 400 CFM at best, its intake sits high and shallow above the back of the range instead of over the front burners, and in many kitchens it recirculates rather than ducts. Over a gas range above 40,000 BTU, or for regular frying, fit a real hood and move the microwave.
How do I end up with a hood I will actually switch on?
Buy for the sone rating at high speed and for where the motor sits. Under about 5 sones on high stays conversational, while 8 or more gets left off. An inline blower in the attic or an exterior blower on the roof takes the noise out of the room and can leave 1 to 3 sones at the cooktop. A variable dial lets you run a quiet setting throughout cooking.
