A ducted range hood pulls cooking exhaust through ductwork to the outdoors, carrying grease, odor and water vapor out of the house with it. A recirculating hood pulls the same air through a grease filter and a charcoal cartridge and blows it straight back into the kitchen — it traps grease and adsorbs some odor, but it removes no moisture at all. Trace the ductwork to find out which one is installed: if there is no duct reaching an exterior wall or the roof, every ounce of steam from every pot stays in the room.
What "ducted" and "recirculating" actually mean
A ducted range hood — also called vented or externally vented — draws air in through the filter above the cooktop and pushes it through rigid or flexible ductwork to a cap on an exterior wall or the roof. Whatever came off the stove — grease droplets, odor compounds, combustion byproducts from a gas burner, water vapor — physically leaves the building.
A recirculating range hood, sometimes labeled ductless or non-vented, uses the same fan and the same grille but has nowhere outside to send the air. Instead it pulls air through an aluminum mesh grease filter, then through a charcoal or carbon cartridge meant to adsorb odor, and blows the filtered air back out the front or top of the hood into the same room it came from. It is common in apartments, rentals and island cooktop installations, where running a duct to the outside is expensive, structurally difficult, or was simply never done.
Why this matters for humidity, not just grease and smell
A pot at a rolling boil or a pan of simmering sauce releases a surprising volume of water vapor in a few minutes, and that vapor stays a gas — it does not stick to a grease filter or get trapped by activated charcoal the way an oil droplet or an odor molecule does. A ducted hood carries that water vapor outside along with everything else in the exhaust stream. A recirculating hood's filters were never built to touch it, so it passes straight through and back into the kitchen, humidity intact.
This is the first thing worth checking on a kitchen window that fogs during cooking, ahead of any habit change: the article on why a kitchen window fogs up when cooking treats confirming the hood type as step one, because no amount of running a recirculating hood longer will remove moisture it was never designed to remove.
How to tell which type is installed
Look for a duct leaving the house
Trace above the hood, through the cabinet it sits under, or up into the ceiling for a rigid or flexible duct that actually reaches an exterior wall or roof cap. A short duct run into the cabinet above that dead-ends is not venting anywhere — it is decorative.
Check for a charcoal filter access panel
Recirculating hoods almost always have a second filter behind or above the grease filter, usually a rectangular cartridge with a charcoal or carbon smell when new. A hood with only a metal grease filter and nothing behind it is more likely ducted.
Feel for airflow outside
With the hood on high, hold a strip of tissue near the exterior wall or roof cap where a duct would terminate. Movement confirms air is leaving the building; no cap to check at all is a strong sign the hood is recirculating.
Pull the model number
Most manufacturers list "ducted," "convertible" or "ductless" directly in the product specifications online. A convertible hood can run either way depending on how it was installed, so the listing alone does not settle it — confirm against what is actually behind the wall.
Treat an island cooktop as recirculating until proven otherwise
A duct run below the floor to an exterior wall is possible but uncommon and expensive, so an island hood or downdraft vent with no visible ductwork above or below is very often recirculating by default.
Ducted vs. recirculating hoods, compared
| Feature | Ducted | Recirculating |
|---|---|---|
| Where the air goes | Outdoors, through ductwork | Back into the kitchen |
| Moisture removed | Yes, all of it that reaches the hood | None |
| Grease removed | Yes, by the metal filter | Yes, by the metal filter |
| Odor reduced | Yes, carried outside entirely | Partially, while the charcoal filter is fresh |
| Gas combustion byproducts | Removed with the rest of the exhaust | Not removed |
| Typical setting | New construction, renovations with duct access | Apartments, rentals, island cooktops |
| Ongoing maintenance | Clean or replace grease filter | Clean grease filter, replace charcoal cartridge |
Why a recirculating hood still feels like it is "venting"
The fan noise, the visible pull of air into the grille, and the light switching on all give the same sensory impression whether the hood is ducted or not, which is exactly why so many people assume a working range hood is removing moisture regardless of type. What the fan is actually doing with a recirculating unit is pulling air through two filters and pushing it back out a few inches away — a loop, not an exit.
The aluminum mesh grease filter works by inertial separation: heavier oil droplets slam into the mesh and stick as the air changes direction around it, while lighter water vapor and odor molecules pass straight through unaffected. The charcoal cartridge behind it works by adsorption, holding certain odor compounds against its enormous internal surface area. Neither mechanism does anything to a gas as light and pervasive as water vapor, which is why a recirculating hood can smell noticeably better after a few minutes of running while doing nothing measurable to the room's humidity.
The retrofit case: converting to ducted
Where a range sits against or near an exterior wall, converting a recirculating hood to ducted is often a matter of cutting a wall penetration, running a short length of rigid duct, and fitting an exterior wall cap with a backdraft damper to keep outside air and pests from coming back in when the fan is off. The payoff is permanent: grease, odor, combustion byproducts and moisture all start leaving the house instead of cycling through it, and the kitchen window stops being the room's most reliable fog alarm.
The retrofit is harder to justify for an island cooktop far from any exterior wall, an upper-floor apartment with no roof access, or a building where the lease or historic-preservation rules block cutting a new penetration. In those cases, a whole-house approach — see whole-house ventilation — can offset some of the moisture a household produces, but it is not a substitute for pulling steam out at the source the moment it is released; point-source extraction and whole-house ventilation solve overlapping but different problems.
Keeping a recirculating hood doing its actual job
A recirculating hood that is never maintained does progressively less even for the two things it can do. Clean the metal grease filter every month or two — most are dishwasher-safe or wipe clean with a degreaser — since a clogged filter reduces airflow through the whole unit and lets more grease drift past into the room and onto nearby cabinets.
Replace the charcoal cartridge every three to six months depending on how often and how heavily the household cooks; a saturated cartridge stops adsorbing new odor but was never doing anything for moisture in the first place, so replacing it restores the odor control without changing the humidity picture at all. A fresh charcoal filter is not a substitute for ducting — it narrows the gap on smell, not on steam.
When a recirculating hood is genuinely fine
A recirculating hood is not a defective product — it was simply never built to remove moisture, and it is not a problem in a household that already handles kitchen humidity another way: cracking the window during heavy cooking in cool weather, running a whole-house ventilation system, or simply cooking lightly enough that the room's baseline humidity rarely climbs far.
The mismatch shows up specifically in a household that cooks with a lot of boiling, steaming or simmering, keeps the kitchen closed off from the rest of the house, and expects the hood alone to keep the window and countertops from fogging or sweating. That household needs either the habits in the next section, a duct retrofit, or both.
The cooking habits that help either type
A lid on a boiling or simmering pot cuts the water vapor it releases dramatically, and it is the one fix that helps a recirculating hood exactly as much as a ducted one, since neither hood type ever has to deal with the steam in the first place. Cracking the kitchen window for a few minutes during the heaviest cooking is the next best move in cool weather, when outdoor air is reliably drier than the saturated air right over the stove.
With a genuinely ducted hood, turn it on before the first burner lights and leave it running ten to fifteen minutes after the last pan comes off, since food and hot surfaces keep releasing moisture for a while after the heat is off. A recirculating hood benefits from the same run-on habit for grease and odor control, even though it will never touch the moisture no matter how long it runs.
When the window keeps fogging regardless
A kitchen window that keeps fogging after the hood has been confirmed ducted, lids are going on pots, and the window is being cracked in cool weather is very likely picking up humidity the rest of the kitchen is contributing outside of cooking — see the kitchen humidity guide for the other sources a kitchen carries, from an unvented dishwasher cycle to a nearby laundry appliance venting indoors.
From there, treat it as a room-wide ventilation question rather than a hood question: the full ventilation guide covers purge airing, background ventilation and whole-house options once source control at the stove is no longer the limiting factor.
Common questions
How can I tell if my range hood is ducted or recirculating?
Trace the ductwork above, behind or below the hood to see whether it actually reaches an exterior wall or the roof. A hood with a charcoal filter cartridge behind the grease filter, or one with no visible duct run anywhere, is almost always recirculating.
Does a recirculating range hood remove any humidity at all?
No. Its grease filter traps oil droplets by inertial separation and its charcoal cartridge adsorbs some odor compounds, but neither mechanism affects water vapor, which passes straight through and back into the room.
Is it worth converting a recirculating range hood to a ducted one?
Where the range sits near an exterior wall and a short duct run with a wall cap is feasible, yes — it permanently removes grease, odor, combustion byproducts and moisture instead of cycling them back into the kitchen. It is harder to justify for an island far from any wall or a rental where cutting a new penetration is not an option.
How often should I replace the charcoal filter in a recirculating hood?
Roughly every three to six months depending on how often and how heavily the household cooks. A fresh cartridge restores odor adsorption, but it does not change how much moisture the hood removes, which is none either way.
Can I just crack a window instead of worrying about which hood I have?
It helps in cool weather, when outdoor air is reliably drier than the saturated air over the stove, but it is a supplement rather than a substitute — a genuinely ducted hood removes steam at the source before it spreads to the rest of the kitchen, which an open window several feet away cannot fully replicate.
Sources
- US EPA — Mold and moisture guidance — the 30–50% range and the 10 sq ft remediation threshold
- ASHRAE Standard 55 — Thermal environmental conditions for human occupancy — indoor comfort and humidity limits
- US DOE 10 CFR 430 — Dehumidifier test procedure — the 2019 move to 65 °F rating conditions
- ASHRAE Standard 62.2 — Ventilation and Acceptable Indoor Air Quality in Residential Buildings — the residential kitchen exhaust rate a ducted range hood is expected to meet; a recirculating hood contributes nothing toward it
- US EPA — A Brief Guide to Mold, Moisture and Your Home — sustained elevated kitchen humidity, uncleared by ventilation, as a condition that supports mold and condensation