What is the best way to ventilate a kitchen?
The best kitchen ventilation is a ducted (vented) range hood mounted over the cooktop that exhausts to the outdoors. It captures grease, smoke, steam, heat, and combustion gases at the source, before they spread into the rest of the house, and sends them outside instead of recirculating them. Nothing else does all four jobs at once, which is why a good hood is the single most useful piece of ventilation a kitchen can have.
Cooking is one of the largest sources of indoor air pollution in a home. Frying and searing throw off fine particulate (PM2.5), a gas burner adds nitrogen dioxide and moisture, and every method releases heat and water vapor that raise indoor humidity. A vented hood pulls that plume out at the moment it forms. An open window or a ceiling fan just stirs it around the room, and a recirculating hood only strains out some grease and odor before blowing the rest back at you.
If your kitchen opens onto the living space, ventilation matters even more, because there is no door to contain the cooking air. In an open floor plan the hood is doing double duty: keeping the air clean and keeping cooking heat from loading up the space your AC has to cool. For that heat side of the equation, size the cooling for the whole open area with the BTU calculator; a big open kitchen adds load your air conditioner has to carry.
Do kitchen hoods need to vent outside?
A range hood works far better when it vents outside, and for a serious cook it should. A ducted hood carries the captured air through a duct to an exterior wall or roof cap and dumps it outdoors. A ductless (recirculating) hood has no duct: it pulls air through a grease filter and a charcoal filter, then pushes it right back into the kitchen. Recirculating removes some grease and odor, but it does nothing for heat, moisture, or combustion gases, because all of that stays in the room.
Ducted is the clear winner on performance, and it is what building codes assume for a real exhaust system. The catch is installation: you need a path to the outside, a smooth metal duct kept as short and straight as possible, and an exterior wall or roof cap with a backdraft damper. Never vent a kitchen hood into an attic, a crawl space, or a soffit; dumping greasy, humid air into those spaces breeds mold and grease buildup, and in many places it is a code violation.
Recirculating hoods exist for a reason: apartments, interior kitchens, and island setups where running a duct outdoors is impractical or expensive. If that is you, a recirculating hood plus an open window and a good air purifier for the fine particulate is a reasonable stopgap. Just know its limits, and change the charcoal filter every few months or it stops absorbing odor and becomes a greasy brick.
How much airflow (CFM) does a kitchen range hood need?
Range hood airflow is measured in CFM (cubic feet per minute), and the right number depends on your stove. The standard rule for an electric range is about 100 CFM per linear foot of cooktop width: a common 30-inch (2.5-foot) range wants roughly 250 CFM, and a 36-inch range wants around 300. Industry guidance also sets a practical floor of about 100 CFM for any hood over a residential range.
Gas cooktops are sized by burner output, not width, because they put out real heat and combustion byproducts. The common rule is about 1 CFM per 100 BTU of total burner rating, so a 40,000-BTU cooktop points to roughly 400 CFM, and a high-output pro-style range with 60,000 BTU or more can call for 600 to 900 CFM. Check the plate on your range for its total BTU rating and size up from there.
Bigger is not automatically better. A hood pulling over about 400 CFM starts to depressurize a tight house, which is where makeup air comes in (more on that below). Mounting height matters too: keep the hood roughly 24 to 30 inches above the cooktop, follow the maker's spec, and pick a hood at least as wide as the range so it actually catches the plume instead of letting it spill around the edges.
What are the rules for kitchen ventilation?
The core code rule is simple: a kitchen exhaust hood has to terminate outdoors, not into an attic, soffit, crawl space, or another room. Residential codes based on the IRC require domestic range hood ducts to be smooth metal (not the flexible plastic used for bathroom fans), airtight, and equipped with a backdraft damper so outside air does not blow back in when the hood is off.
The rule that surprises people is makeup air. Most residential codes, following the International Residential Code, require a makeup air system once an exhaust hood exceeds about 400 CFM. That is because a hood that strong pulls out more air than a house can naturally replace, and the resulting negative pressure can be dangerous around gas appliances. Whether you need a permit depends on your jurisdiction; adding or replacing a ducted hood, and especially adding makeup air, often does.
There is no single national standard for every situation, so your local building department has the final say, and requirements are stricter for gas and for very tight, newer homes. If you are planning a remodel or a high-output range, ask the department (or your installer) about makeup air and permits before you buy the hood, not after. Getting the airflow and the makeup air matched is the part worth doing right.
What is makeup air, and when do you need it?
Makeup air is replacement air brought into the house to balance what a powerful range hood pulls out. A hood is an exhaust fan; every cubic foot it blows outside has to be replaced by a cubic foot coming in from somewhere. In a leaky old house, that air sneaks in through gaps. In a tight, well-sealed house, there is nowhere for it to come from, so the whole house goes into negative pressure.
That negative pressure is the real hazard, and it is why this is not a casual DIY topic. When a house is depressurized, it can backdraft a natural-draft gas furnace or water heater, meaning combustion gases (including carbon monoxide) get pulled back down the flue and into your living space instead of going up the chimney. A hood over roughly 400 CFM in a tight home with atmospheric gas appliances is exactly the setup where this happens, which is why code ties makeup air to that threshold.
A makeup air system is a ducted intake, often with a motorized damper that opens when the hood turns on and sometimes a small heater so the incoming winter air is not freezing. Sizing and interlocking it with the hood, and confirming the house is not backdrafting, is measurement-and-combustion work for a licensed HVAC pro. At minimum, keep a working CO alarm near sleeping areas, and if you run gas and a strong hood, get makeup air assessed. If you are already adding whole-home fresh air, an ERV is a related balanced-ventilation approach, though it is not a substitute for dedicated makeup air on a big hood.
How do you ventilate a kitchen without a range hood?
If you cannot install a hood, you can still cut the cooking load, just not as well. Open a window and put a box fan in it facing outward to create real exhaust, ideally with a second window cracked across the room so fresh air has a path in. This crossflow actually removes air rather than just circulating it, and it is the most effective no-hood option for smoke and steam.
Beyond that, use what you have and manage the source. Run any nearby bathroom or whole-house exhaust fan while you cook, use the back burners (a hood or a window pulls their plume more directly), keep lids on pots to cut steam, and avoid long high-heat frying when you cannot ventilate. A recirculating hood or an over-the-range microwave set to recirculate will catch some grease and odor, but remember it does nothing for heat, moisture, or gas byproducts.
For the fine particulate that cooking throws off, a HEPA [air purifier](/reviews/best-air-purifiers) sized to the space helps clear PM2.5 after the fact, and it is worth having in an open-plan kitchen. What a purifier cannot do is remove moisture, heat, or carbon monoxide, so it complements ventilation rather than replacing it. The order of preference stays the same: a ducted hood first, real crossflow ventilation second, and recirculating plus filtration as the backup when neither is possible.
Frequently asked questions
What is the best ventilation for a kitchen?
A ducted range hood that vents outdoors, sized to your stove and mounted directly over the cooktop. It captures grease, smoke, steam, heat, and combustion gases at the source and removes them from the house, which no other method does all at once. An open window or a recirculating hood is a weaker backup that moves air around without fully getting the cooking byproducts out.
What are the rules for kitchen ventilation?
A kitchen exhaust hood must terminate outdoors (never into an attic, soffit, or crawl space), the duct must be smooth metal with a backdraft damper, and once a hood exceeds about 400 CFM most residential codes following the IRC require a makeup air system. Requirements are stricter for gas and for tight newer homes, and many jurisdictions require a permit. Your local building department has the final say, so confirm before you buy a high-output hood.
Do kitchen hoods need outside venting?
For real performance, yes. A ducted hood that vents outside removes heat, moisture, grease, and combustion gases; a ductless (recirculating) hood only filters some grease and odor and blows the rest back into the room, so heat and humidity stay indoors. Recirculating hoods make sense for apartments and interior or island kitchens where running a duct outdoors is not practical, but a vented hood is always the better ventilation.
What are the ways to ventilate a kitchen?
In order of effectiveness: a ducted range hood vented outdoors (best), real crossflow with a box fan exhausting out a window and a second window cracked for intake, running nearby bathroom or whole-house exhaust fans while you cook, and a recirculating hood plus a HEPA air purifier for particulate as a last resort. Source control (back burners, lids on pots, less high-heat frying) helps in every case.
Is a ductless recirculating range hood worth it?
It is worth it only when you cannot duct to the outside, such as an apartment or an island cooktop. A recirculating hood traps some grease and, with a charcoal filter, some odor, but it does nothing for heat, moisture, or combustion gases, and the charcoal filter needs replacing every few months. If you have any path to an exterior wall or roof, a ducted hood is a much better use of the same money.