TL;DR
A ducted range hood that vents outside genuinely removes cooking particulate, moisture, and combustion byproducts from the house. A recirculating hood filters grease and some odor and then returns everything else -- including moisture and gases -- to the room. Whether a hood helps depends almost entirely on which of those two you have, and on whether anyone actually turns it on.
Cooking is one of the largest indoor pollution sources in a home
Frying, searing, broiling, and toasting all release fine particles. Gas burners add combustion byproducts on top of whatever the food produces. Boiling adds a substantial amount of water vapor.
Public agencies consistently identify cooking as a significant source of indoor particulate in residences, which is why kitchen ventilation is treated as a building requirement rather than a convenience.
Source: Public health and building science guidance on residential kitchen ventilation
Do range hoods actually work?
A ducted hood that vents outdoors works well when it is sized correctly and turned on. It removes particulate, moisture, grease aerosol, and combustion gases from the building. A recirculating hood removes grease and some odor with filters, then returns the air -- so moisture and gases stay in the kitchen.
Ducted versus recirculating, plainly
| Feature | Ducted hood | Recirculating hood |
|---|---|---|
| Grease aerosol | Removed from the house | Captured by a grease filter |
| Odors | Removed | Reduced by a charcoal filter, temporarily |
| Fine particulate | Removed | Mostly returned to the room |
| Moisture | Removed | Returned to the room |
| Combustion gases | Removed | Returned to the room |
| Filter cost over time | Grease filter, washable | Charcoal filters, replaced regularly |
| Install requirement | Duct to the exterior | None |
A recirculating hood is better than nothing -- it keeps grease off cabinets and takes the edge off odors. It is not an air quality solution, and it should not be described as one. If you are choosing between them and a duct run is possible, ducted is the meaningful upgrade.
Does a range hood need to be vented outside?
For it to actually remove anything from the home, yes. A ducted hood must terminate outdoors -- not into an attic, a soffit, a crawl space, or a cabinet. Venting into an attic moves grease and moisture into the structure, where it causes staining, damp insulation, and long-term damage.
Capture rate is the number that matters
A hood is only as good as the share of the plume it catches, and that share is set by physics you can influence.
Coverage. A hood that is narrower than the cooktop misses the plume from the outside burners. Matching the width, or overhanging slightly, catches far more.
Height. Mounted too high, the plume spreads before it reaches the hood. Too low is a fire and clearance issue. Follow the manufacturer's specified range.
Which burner you use. Back burners sit further under most hoods and are captured much better than front burners. This one costs nothing and makes a real difference.
Fan speed. Low is quiet and captures little from a hard sear. Use a speed that matches the cooking.
Timing. Turn the hood on before you start and leave it running for ten to fifteen minutes after you finish, the same principle as running a bathroom fan after a shower -- covered in how long to run a bathroom exhaust fan.
Makeup air. A very powerful hood in a tight house can pull more air out than the building can replace, which affects how the hood performs and can matter for any combustion appliance in the home. Cracking a window nearby helps, and high-capacity hoods often require a dedicated makeup air system by code.
Filters are the maintenance the hood actually needs
A grease filter that is loaded stops pulling air through, which drops the capture rate regardless of how strong the fan is.
Metal mesh and baffle filters are washable. Degrease them in hot water with dish soap, or run mesh filters through a dishwasher if the manufacturer allows it. Monthly is a reasonable cadence for regular cooking. The full method is in how to clean range hood filters.
Charcoal filters in recirculating hoods are not washable. They adsorb odor until they are saturated, and then they do nothing. Replace them on the schedule in the manual, typically a few times a year.
The hood housing, the fan blades, and the duct opening also accumulate grease. Greasy dust binds to surfaces and needs a degreaser rather than a duster, which is why kitchen high surfaces are their own job -- see cleaning a greasy kitchen exhaust fan and high dusting cabinet tops and doors.
Never mix cleaning products while degreasing, and never combine bleach with anything containing ammonia, acid, or alcohol. Work with the hood switched off and ventilate the room.
What a hood does not solve
An over-the-range microwave with a built-in fan is often set to recirculate rather than duct, even when a duct exists behind it. Many are installed in recirculating mode by default. Checking which mode yours is in takes a minute and changes what the appliance is actually doing.
A hood also does not address anything outside the kitchen. It treats the plume above the cooktop, and only while it is running.
The health framing, kept honest
Good kitchen ventilation reduces exposure to cooking particulate, moisture, and combustion byproducts. Reducing exposure is a sensible goal, and building codes require kitchen ventilation for that reason.
It does not treat, prevent, or cure asthma, allergies, respiratory illness, or any other condition, and no appliance claim to the contrary should be trusted. If someone in the household has symptoms that seem tied to cooking, that is a question for a doctor.
If a gas appliance produces soot, a persistent smell, or symptoms in the home, stop using it and have it inspected by a qualified technician. Working carbon monoxide alarms are a separate and non-negotiable safety item in any home with fuel-burning appliances.
FAQ
Does a range hood really improve indoor air quality?
A ducted hood that vents outside does -- it removes cooking particulate, grease aerosol, moisture, and combustion byproducts from the building. A recirculating hood filters grease and some odor and returns the rest to the room, so it improves cleanliness far more than it improves air quality.
Does a range hood have to be vented outside?
To actually remove anything from the home, yes. The duct must terminate outdoors, never into an attic, soffit, crawl space, or cabinet. Venting into an attic pushes grease and moisture into the structure, which causes staining, damp insulation, and long-term damage over time.
Are recirculating range hoods worth it?
They are better than nothing. They keep grease off cabinets and reduce odor while the charcoal filter is fresh. They do not remove moisture, fine particulate, or combustion gases from the room. If a duct run to the exterior is possible, that upgrade is the one that changes air quality.
When should you turn on a range hood?
Turn it on before you start cooking and leave it running ten to fifteen minutes after you finish. Starting early captures the plume from the beginning, and running afterward clears what is still airborne. Using back burners rather than front ones also improves capture noticeably.
How often should range hood filters be cleaned?
Metal mesh and baffle grease filters do well cleaned monthly with regular cooking, in hot water with dish soap or in a dishwasher where the manufacturer allows it. Charcoal filters in recirculating hoods cannot be washed and are replaced on the manual's schedule, usually a few times a year.
Does a range hood help with gas stove emissions?
A ducted hood removes combustion byproducts from the building along with the cooking plume, which reduces exposure. A recirculating hood does not. Using back burners, running the fan at an adequate speed, and keeping filters clean all improve capture. Health questions belong with a doctor.
Kitchen grease is the hardest household soil to keep ahead of, and it accumulates on hoods, cabinet tops, and everything nearby. If you want that handled on a schedule, get a quote or read more about house cleaning services.