Cooking generates combustion byproducts, grease particles, moisture, and volatile organic compounds — regardless of whether you cook with gas or electric. A range hood that vents to the exterior removes these pollutants from the kitchen air before they disperse through the home. A recirculating hood filters some grease and odor but returns the air — and everything else in it — back into the room. The difference between the two is the difference between removing pollutants and rearranging them.
What Cooking Actually Produces
Gas cooking releases nitrogen dioxide (NO2), carbon monoxide (CO), and formaldehyde as combustion byproducts — compounds that are regulated in outdoor air but completely unregulated inside your kitchen. A landmark study from Lawrence Berkeley National Laboratory found that using a single gas burner without ventilation can produce nitrogen dioxide levels that exceed EPA outdoor air quality standards within minutes. In homes where multiple burners and the oven operate simultaneously, concentrations can reach levels associated with respiratory inflammation, particularly in children and people with asthma.
Electric cooking produces fewer combustion byproducts but still generates significant particulate matter from heated oils, fats, and food surfaces. Ultrafine particles — too small to see but small enough to penetrate deep into the lungs and cross into the bloodstream — are produced whenever oil reaches its smoke point. All cooking generates moisture that raises indoor humidity, which in turn promotes mold growth and increases off-gassing rates from building materials throughout the home.
Exterior Venting vs. Recirculating
An exterior-venting range hood captures pollutants at the cooktop surface and exhausts them through ductwork to the outside of the home. The air leaves. A recirculating hood passes air through a charcoal filter that captures some grease particles and some odor molecules, then blows the air back into the kitchen. The charcoal filter does not remove nitrogen dioxide, carbon monoxide, moisture, formaldehyde, or ultrafine particles. These pass through the filter and return to the room.
If your kitchen allows exterior venting — and the vast majority of kitchens do, through a wall cap or roof vent — it is always the better choice. The hood should cover the entire cooktop surface and be mounted 24–30 inches above the cooking surface. Minimum recommended capacity is 100 CFM per linear foot of cooktop. And the fan must be used every time you cook — not just when something is visibly smoking. The pollutants are produced by normal cooking at normal temperatures, not just by burnt food.
Where To Start
- Verify whether your hood vents outside. Check for ductwork to an exterior wall or roof cap.
- Use the hood every time you cook. Combustion byproducts and moisture are produced by all cooking.
- If renovating, specify exterior-venting. The single most impactful kitchen air quality upgrade.
The range hood is the exhaust fan of the kitchen. Like the bathroom exhaust fan, it only protects the air when it runs. Using it consistently — from the moment the burner ignites until several minutes after cooking ends — is one of the simplest ways to protect the air quality of the room where you prepare food for your family.
Does your range hood vent to the outside — and do you turn it on every time you cook?