Kitchen Exhaust Air Duct: My Guide to a Healthier Home: 1 Minute to Understand the Smartest Kitchen Ventilation Solutions

Good kitchen ventilation starts long before the range hood arrives. The way an exhaust air duct is sized, routed, and terminated determines whether smoke, grease, moisture, and odors leave the home—or linger. In my projects, a properly designed duct consistently reduces cooking byproducts and keeps finishes from yellowing. WELL v2 recommends continuous source control and adequate exhaust for kitchens, and it ties effective ventilation to better indoor air quality metrics, including PM2.5 and VOC reduction (WELL v2 Air concept). Steelcase research also associates improved air quality with measurable gains in cognitive performance; their studies link fresher air to better focus and decision-making in work settings, and the principle applies at home when kitchens share open plans with living spaces.

The physics are simple: move enough air, move it efficiently, and don’t reintroduce contaminants. For residential range hoods, typical capture rates span 150–600 CFM for electric cooktops and 300–900 CFM for gas, depending on cooking intensity and hood geometry. I look at cooking style first: frequent high-heat searing or wok cooking pushes me to 700–900 CFM with a make-up air strategy. For duct performance, friction losses in long runs or multiple elbows can cut delivered CFM by 20–40%, so minimizing equivalent length is critical. I follow published guidance on illumination as well; the Illuminating Engineering Society (IES) recommends about 300–500 lux on kitchen counters to improve task visibility, which indirectly supports safer, cleaner cooking by helping users spot smoke, splatter, and residue. For workplace-backed evidence on environment and performance, Gensler’s research indicates environments with controlled sensory loads—air, light, sound—improve task effectiveness, a helpful benchmark for open-plan homes where kitchens anchor daily routines. Learn more from Steelcase’s research on air and performance.

Assessing Your Kitchen and Setting Ventilation Goals

I start with three factors: appliance type, cooking behavior, and room adjacency. Gas cooktops generate combustion byproducts (NO2, CO, ultrafine particles), which makes ducted exhaust non-negotiable. If your kitchen opens to a living area, odors and moisture spread quickly; target higher capture efficiency and a quiet system that can run longer without fatigue. When a client sautés daily, I specify a deep, wide hood with 90–110% cooktop width coverage and a duct that preserves as much of the rated CFM as possible.

Choosing Ducted vs. Recirculating

Recirculating hoods filter and return air to the room. They can reduce odors but do little for moisture and combustion byproducts. For health and durability, ducted exhaust is the gold standard. Charcoal filters in recirculating systems require frequent replacement to remain effective, and even then, humidity stays in the space—bad for cabinetry and finishes. If ducting outdoors is structurally challenging, I still explore creative routing to reach an exterior wall or roof.

Right-Sizing the Duct and Fan

A mismatch between fan and duct is the most common failure I see. Undersized ducts raise static pressure, increase noise, and slash airflow. As a rule of thumb for residential systems: a 6-inch round (or equivalent) duct suits ~300–400 CFM; 7-inch for ~500–600 CFM; 8-inch for ~650–900 CFM. Keep velocity between roughly 700–1,200 fpm to balance capture and noise. If you need 900 CFM for heavy wok cooking, plan on 8-inch ducting with minimal bends and a high-quality, back-draft damper.

Routing: Short, Straight, and Smart

The duct run should be as short and straight as architecture allows. Every elbow adds equivalent length; tight 90° turns are more punishing than long-radius bends. I cap total equivalent length at about 35–50 feet for most residential hoods, but prefer far less. Roof terminations often perform better than challenging sidewall routes. When planning a renovation, I simulate layout options and heights to minimize bends. A simple interior layout planner like this room layout tool can help visualize hood placement, ceiling drops, and chase routing to avoid structural conflicts.

Make-Up Air: The Hidden Partner

High-CFM systems need make-up air to prevent depressurization. Without it, the hood struggles, doors slam, and combustion appliances risk back-drafting. I coordinate a dedicated make-up air inlet—tempered when climate demands—with interlock controls that open when the hood runs above a set speed. In cold regions, tempering the incoming air avoids discomfort and condensation.

Noise, Comfort, and Everyday Usability

Performance doesn’t matter if users won’t switch the hood on. I aim for 1.5–3.0 sones at typical cooking speeds and use remote in-line or external fans to cut noise at the cooktop. Smooth-walled metal ducting, sealed joints, and anti-vibration mounts help. Acoustic comfort keeps conversations pleasant in open kitchens, encouraging longer ventilation cycles after cooking.

Grease, Moisture, and Materials

Grease quickly coats duct interiors, so I specify baffle filters (dishwasher-safe) and smooth duct interiors, avoiding flex except for tiny connections. Exterior terminations need bird screens that won’t clog; overly fine mesh increases resistance and invites maintenance headaches. Moisture removal protects cabinets and paint. I favor durable, low-VOC finishes and sealants around hoods and duct chases so cleaning doesn’t degrade surfaces, aligning with healthy-home goals.

Placement and Hood Geometry

Capture depends on geometry. A deeper hood with good side containment and the right height—typically 26–30 inches above the cooking surface for wall-mount units—does a better job corralling plumes. Island hoods benefit from larger canopies and higher CFM because cross-drafts are harder to control. If ceilings are tall, adding a partial baffle or shelf behind the cooktop can tame air currents.

Controls, Sensors, and Lighting

Variable speed control is non-negotiable; most cooking doesn’t need maximum draw. I sometimes add a simple timer or VOC/PM sensor integration to encourage post-cook ventilation for 10–20 minutes. Task lighting matters as much as airflow. Target around 300–500 lux on counters with warm-neutral 3000–3500K color temperature to keep food looking natural and reduce glare while prepping, per IES task-lighting guidance.

Safety and Code Considerations

Respect clearances to combustibles, ensure a listed back-draft damper at the termination, and keep the duct path outside of sleeping rooms when possible. For gas ranges near fire suppression systems or alarm detectors, coordinate placement to avoid false triggers. Check local jurisdiction requirements for make-up air thresholds—many trigger at and above 400–600 CFM.

Maintenance: Keep It Performing

Ventilation is a system, not a single product. Quarterly filter cleaning, annual duct inspection, and verification of damper operation keep performance near spec. If capture feels weaker over time, look for blockages, loose joints, or tired fans. A small maintenance routine sustains the healthier-home benefits you invested in.

Design Integration in Renovations

When I plan a renovation, I align cabinet depths, hood geometry, and chase locations early. I’ll prototype duct routes in a layout simulation tool to avoid structural conflicts, balance run length, and preserve ceiling aesthetics. If an island hood is essential, I budget for larger duct diameter and an external fan to keep noise out of social zones.

FAQ

How many CFM do I really need?

Match CFM to cooking intensity and hood geometry. Light electric cooking may be fine at 250–350 CFM, while frequent high-heat gas or wok cooking often benefits from 700–900 CFM and make-up air.

What duct size should I use?

Use 6-inch for ~300–400 CFM, 7-inch for ~500–600 CFM, and 8-inch for ~650–900 CFM. Keep runs short and minimize elbows to preserve delivered airflow.

Is a recirculating hood enough?

It helps with odors but not moisture or combustion byproducts. For health and durability, a ducted exhaust to the exterior is the better choice.

Do I need make-up air?

Above ~400–600 CFM many jurisdictions require it. Even when not required, make-up air improves performance and prevents negative pressure and back-drafting.

How can I reduce noise?

Use larger ducts, smooth interior metal, remote in-line or external fans, and quality baffle filters. Proper sizing lowers static pressure and sones.

What’s the ideal hood mounting height?

Typically 26–30 inches above the cooktop for wall hoods; island hoods may need a wider canopy or higher CFM due to cross-drafts.

Which filters are best?

Baffle filters capture grease efficiently and are easy to clean. Replace or clean regularly; charcoal filters in recirculating systems must be changed often to remain effective.

How much lighting do I need?

Aim for 300–500 lux on counters with 3000–3500K color temperature for clear, comfortable task visibility, in line with IES guidance.

Can I use flexible ducting?

Avoid long flex runs. Use smooth metal ducting to minimize resistance and grease buildup; flex only for short transitions if necessary.

What about outdoor terminations?

Choose a termination cap with a reliable back-draft damper and bird guard that won’t clog. Maintain clearance from soffits to prevent re-entrainment.