What rises off the burners
Every kind of cooking releases moisture. High-heat cooking adds smoke and a fine mist of grease that settles on cabinet tops, light fixtures and the ceiling over months. Browning and charring add odor that clings to fabric in the next room. Where that mixture goes next is the whole question of range hood and indoor air quality.
Gas burners add something the others do not: combustion products. EPA lists unvented combustion appliances such as gas stoves among the main indoor sources of nitrogen dioxide, an irritant for the eyes, nose, throat and airways. It notes that in homes with gas cooking, indoor levels often exceed outdoor levels.
Who notices it first
EPA's page on nitrogen dioxide lists increased airway reactivity in some people with asthma, reduced lung function in people with chronic obstructive pulmonary disease and a higher risk of respiratory infections in young children among the effects of low-level exposure. A household with any of those has the strongest reason to run a ducted hood every time.
Electric and induction surfaces
Taking the flame away removes the combustion gases but not the rest. Oil still smokes at the same temperature on induction, and a pot of pasta releases as much steam on a radiant element as on a burner. The hood's job shrinks; it does not disappear.
Source: EPA — Nitrogen Dioxide's Impact on Indoor Air Quality — Unvented combustion appliances such as gas stoves are a primary indoor source of NO2; indoor levels in homes with gas stoves often exceed outdoor levels; low-level exposure effects; install and use an exhaust fan vented to outdoors over gas stoves
Ducted and recirculating hoods do different jobs
A ducted hood pushes air through metal duct to a cap on the roof or an outside wall. EPA describes kitchen fans that exhaust outdoors as removing contaminants directly from the room and raising the home's outdoor air ventilation rate at the same time.
A recirculating hood draws air through a grease filter and a charcoal filter and blows it back into the kitchen. It catches grease and reduces odor while the charcoal is fresh, but the steam, the heat and any combustion gases come straight back out. HVI's guidance is blunt: nonducted, recirculation hoods provide no actual ventilation.
- Ducted: removes smoke, grease mist, steam, odor and combustion gases from the house.
- Recirculating: traps grease and some odor, returns moisture and gases to the room.
- Downdraft: pulls sideways at the surface, and HVI notes it needs more airflow to capture as well.
When there is no way to the outside
In a condo with no exterior wall, or under a floor above that cannot be opened, a recirculating hood may be the only choice. It is still worth running, as long as the charcoal is changed on the maker's schedule. Pair it with a window cracked open or another exhaust fan in the home when you cook at high heat.
Source: EPA — Improving Indoor Air Quality — Kitchen fans that exhaust outdoors remove contaminants directly from the room and increase the outdoor air ventilation rate; cooking is a short-term activity that can generate high levels of pollutants; Home Ventilating Institute — How Much Ventilation Do I Need? — Canopy hoods capture the rising column of air; downdraft exhausters need higher airflow and cannot equal them; nonducted recirculation hoods provide no actual ventilation
Getting real capture out of the hood you have
A hood can only exhaust what reaches it. Smoke and steam rise in a plume that widens as it climbs and drifts with any draft from a door or a ceiling fan. HVI explains that canopy hoods work well because they catch that rising column; the lower and wider the canopy relative to the burners, the less escapes around its edges.
Clean filters matter as much as fan speed. A mesh filter matted with grease or a baffle filter with its channels filled chokes the airflow, and the blower then moves less air while sounding exactly as loud.
- Switch the hood on when the burners go on, not when the smoke appears.
- Use the rear burners for frying and searing where the canopy reaches farther over them.
- Choose a higher speed for high-heat cooking and a low one for simmering.
- Leave it running after the pans come off until the steam and smell have cleared.
- Wash or replace the filters on the schedule in the use-and-care manual.
The quiet setting that does nothing
Many owners run the lowest speed because the higher ones are loud. For a simmering pot that is fine. For a steak in a hot skillet it moves a fraction of the air the plume carries, and most of the smoke rolls past the front edge of the canopy into the room.
Source: Home Ventilating Institute — How Much Ventilation Do I Need? — Canopy hoods capture the rising column of air; downdraft exhausters need higher airflow and cannot equal them; nonducted recirculation hoods provide no actual ventilation
Moisture, grease film and the rest of the house
ENERGY STAR points out that adequate ventilation helps control moisture and remove odors. In a kitchen that means fewer foggy windows in winter, less condensation on cold exterior walls and less of the sticky film that builds on top of wall cabinets.
That film is a useful gauge. If cabinet tops, the ceiling above the burners or the blades of a nearby ceiling fan are tacky with grease, the hood is not catching what it should, whether because of its speed, its filters, its size or a duct that barely moves air.
Source: ENERGY STAR — Ventilation Fans — Adequate ventilation helps control moisture and remove objectionable odors
Signs the ventilation is falling short
A hood that sounds normal can still be moving very little air. Put a wide pot of water on a front burner, bring it to a boil and switch the hood to high: then watch the steam. If most of it curls out past the front edge of the canopy with clean filters in place, the damper, the duct or the blower is holding the flow back.
What points to a repair rather than a habit
- Smoke rolling out past the canopy even on the highest speed.
- Steam from a boiling pot escaping the canopy on high with clean filters.
- No air movement felt at the outside wall or roof cap when the hood runs.
- Grease dripping from the canopy seams onto the burners.
- A damper flap that rattles or lets cold air in when the hood is off.
