Range Hood Installation: Ducted vs Ductless, Sizing, and Venting Through Walls or Roof

A range hood removes cooking smoke, grease, moisture, and combustion byproducts from your kitchen. The difference between a hood that works and one that just makes noise comes down to three things: adequate airflow for your cooktop, a properly sized and routed duct, and makeup air so the hood can actually pull. Most range hoods underperform not because the fan is too small, but because the ductwork restricts airflow or the house is too tight for the hood to exhaust at its rated capacity. This guide walks through every decision point, from sizing the fan to running the duct to handling makeup air requirements.

Sizing the Hood and Fan

The hood should be at least as wide as the cooktop. Wider is better for capturing smoke and steam that drifts off the front burners. For a standard 30-inch range, use a 30-inch or 36-inch hood. For a 36-inch cooktop, a 42-inch hood provides noticeably better capture, especially on the burners closest to the cook. If you are choosing between two sizes, go wider. The cost difference is usually modest, and the performance difference is significant.

Fan capacity is measured in CFM (cubic feet per minute). For electric cooktops, the baseline recommendation is 100 CFM per linear foot of cooktop width. That means 300 CFM for a 30-inch range and 400 CFM for a 48-inch cooktop. Gas cooktops generate more heat and combustion byproducts, so they need more airflow. Add together the BTU ratings of all burners, divide by 100, and use that as your minimum CFM. A range with four burners totaling 60,000 BTU needs at least 600 CFM.

Mounting height matters more than most people realize. Manufacturers typically specify 24 to 30 inches above an electric cooktop and 30 to 36 inches above gas. Mounting too high reduces capture effectiveness dramatically. Every inch above the recommended range lets more cooking byproducts escape around the edges of the hood. Mounting too low creates a fire hazard, blocks your view of the back burners, and makes working at the stove uncomfortable for anyone over about 5 feet 6 inches tall.

Professional-style ranges with high-output burners (15,000 BTU or more per burner) need commercial-grade ventilation. Budget accordingly. The hood and installation for a pro-style range can easily cost more than the range itself, especially if the duct run is long or goes through the roof. A 1,200 CFM hood with proper ductwork, makeup air, and electrical work can run $3,000 to $6,000 installed.

Ducted vs Ductless

Ducted hoods exhaust air to the outdoors. They remove heat, moisture, grease, and combustion gases from the kitchen entirely. This is the only type that actually ventilates your kitchen. Every building code for new construction requires ducted ventilation for gas cooktops, and for good reason: gas burners produce carbon monoxide, nitrogen dioxide, and water vapor that need to leave the house.

Ductless (recirculating) hoods filter the air through charcoal filters and blow it back into the kitchen. They capture some grease particles and reduce odors, but they cannot remove heat, moisture, or combustion byproducts. The air stays inside. Think of a ductless hood as a last resort for situations where running a duct to the exterior is physically impossible, such as a condo on the 15th floor of a building with no available chase. If you have a gas cooktop and a ductless hood, you should be opening a window every time you cook.

The charcoal filters in ductless hoods need replacement every 3 to 6 months with regular cooking, and more often if you cook frequently or fry often. They cannot be washed or cleaned. Replacement filters typically run $15 to $40 per set, depending on the brand. Over ten years, that adds up to $300 to $800 in filter costs alone. A ducted hood with washable aluminum mesh grease filters has essentially zero ongoing cost. Pull the filters out, run them through the dishwasher or soak them in degreaser, and reinstall.

If you currently have a ductless hood and want to upgrade to ducted, the biggest project cost is not the hood itself. It is cutting through the wall or ceiling to run ductwork to the building exterior. This is the part most homeowners underestimate, both in complexity and in cost. Expect $500 to $1,500 just for the duct installation on a straightforward wall penetration, and significantly more if the duct needs to travel through a cabinet, soffit, attic, or up through the roof.

Ductwork Sizing and Routing

Use rigid smooth-wall duct for range hood exhaust. Never use flexible duct. Flex duct has corrugated interior surfaces that trap grease and dramatically increase air resistance. A 10-foot run of flex duct can have the same friction as 25 to 30 feet of smooth rigid duct. Grease buildup in flex duct is also a fire hazard. If your existing installation uses flex duct, replace it with rigid when you install a new hood.

Match the duct diameter to the hood outlet. Most residential hoods use 6-inch round duct or 3.25-by-10-inch rectangular duct. Never reduce the duct size below the hood outlet. Connecting a 6-inch hood to 4-inch duct (to fit through an existing hole) cuts the effective airflow roughly in half. It is always better to enlarge the wall opening than to reduce the duct. You can transition from round to rectangular to fit through wall cavities, but maintain equivalent cross-sectional area. A 6-inch round duct (about 28 square inches) transitions to a 3.25-by-10-inch rectangular duct (about 32 square inches) without restriction.

Keep duct runs as short and straight as possible. Every 90-degree elbow adds roughly 5 feet of equivalent length. Every foot of duct adds friction loss. Most hoods specify a maximum equivalent duct length, typically 25 to 40 feet depending on the model and fan power. A straight shot through the wall directly behind the hood is ideal. A run that goes up through a cabinet, across the ceiling, through the attic, and out through a roof cap adds 15 to 20 feet of equivalent length plus three or four elbows, which can easily exceed the hood's maximum specification. If your planned route exceeds the hood's maximum duct length, you need a more powerful fan.

Install a wall cap or roof cap with a backdraft damper at the termination point. The damper prevents cold air, wind, insects, and animals from entering through the duct when the hood is off. Clean the cap annually. Grease accumulates on the damper flap and can prevent it from closing fully, which means you have a 6-inch hole in your building envelope leaking conditioned air 24 hours a day. A quick wipe with degreaser during spring cleaning keeps it functioning properly.

Makeup Air Requirements

Any hood exhausting more than 400 CFM typically requires a makeup air system. This is a powered damper that opens when the hood turns on, allowing outside air to enter the house to replace the volume being exhausted. Without makeup air, a powerful hood depressurizes the building. This causes doors that are difficult to open, whistling from window frames, and most seriously, it can back-draft combustion appliances like gas water heaters and furnaces, pulling carbon monoxide into the living space.

Check your local building code for the exact threshold. The International Mechanical Code (IMC) and International Residential Code (IRC) set the threshold at 400 CFM for range hoods in tightly constructed homes. Some jurisdictions set it lower, and some apply the requirement to all new construction regardless of hood CFM. Your permit inspector will know the local rule.

Makeup air kits are available from most hood manufacturers. They typically include a motorized damper that installs in the wall or ductwork, a relay that ties into the hood's fan switch, and a filter. When you turn on the hood, the relay opens the damper. When you turn off the hood, the damper closes. This is the most common residential solution and typically costs $200 to $600 for the kit, plus installation labor.

A simpler but less comfortable approach is a passive makeup air inlet. This is a duct with a manually operated damper that you open when cooking and close when done. The downside is that it lets in unconditioned outside air. In January in Minneapolis, that means 0-degree air blowing into your kitchen. In August in Houston, that means hot, humid air. A powered system with tempered (heated or cooled) makeup air is more comfortable but significantly more expensive, often $1,500 to $3,000 for the full system.

Installation Steps for a Wall-Vent Under-Cabinet Hood

Turn off power to the existing hood or the circuit you will connect to at the breaker panel. Verify the circuit is dead with a non-contact voltage tester at the junction box or outlet where the hood connects. Do not skip this step.

Hold the new hood in position (or tape the mounting template included with most hoods to the cabinet bottom) and mark the duct outlet location on the wall. Also mark the mounting screw locations on the cabinet bottom or wall. If the duct goes through the cabinet above the hood, mark the cabinet bottom for the duct opening as well.

Cut the duct opening through the exterior wall. For a standard wood-framed wall, this means cutting through drywall, insulation, sheathing, and siding. A 6-inch duct needs a 6-1/4 to 6-1/2 inch hole for clearance. Use a reciprocating saw to cut through wood sheathing and a hole saw or jigsaw for siding, depending on the material. For brick or stone veneer, you will need a masonry hole saw or an angle grinder with a diamond blade. Take care not to cut any electrical wires or plumbing in the wall. Use a stud finder that detects wires, or drill a small pilot hole and probe with a coat hanger first.

Install the wall cap from outside. Apply a generous bead of exterior-grade silicone or polyurethane caulk around the flange before screwing it to the siding. Connect the duct from the wall cap to the hood outlet using rigid duct sections and aluminum foil tape at every joint. Do not use standard cloth duct tape. It dries out and fails within a year or two in the heat from cooking exhaust. Support horizontal duct runs every 4 feet with hanging straps to prevent sagging.

Mount the hood to the cabinet bottom or wall brackets using the hardware provided. Connect the electrical wiring. Most hoods either plug into a standard 120V outlet inside the cabinet above, or hardwire to a junction box. Follow the manufacturer's wiring diagram. Restore power at the breaker and test all fan speeds and the light. Run the fan on high and hold a piece of tissue paper near the front edge of the hood. If the hood is working properly, the tissue should pull toward the hood. If it flutters away or hangs limp, check the ductwork for disconnections or obstructions.

Common Installation Mistakes

Using flex duct. This is the single most common mistake. Flexible duct traps grease in its corrugations, restricts airflow by 30 to 50 percent compared to smooth rigid duct, and creates a fire risk. If your existing hood uses flex duct, replace it with rigid when installing the new hood. The extra cost and effort are minimal compared to the performance gain.

Venting into the attic. Never exhaust a range hood into the attic or any enclosed space. The moisture and grease cause mold growth on roof sheathing, wood rot in framing, and a significant fire hazard from grease accumulation. The duct must always terminate at the building exterior through a proper wall cap or roof cap. This is a building code violation in every jurisdiction.

Undersizing the duct. Transitioning a 6-inch hood outlet to 4-inch duct to fit through an existing wall opening is a common shortcut that kills performance. The restriction cuts effective airflow roughly in half. Enlarge the opening instead. A few minutes with a reciprocating saw costs nothing compared to a hood that never works at its rated capacity.

Forgetting the backdraft damper. Without a backdraft damper at the wall or roof cap, cold air pours through the duct in winter, you hear wind noise on breezy days, and insects may find their way in during summer. Most quality wall caps and roof caps include a built-in damper, but some inexpensive models do not. Check before you buy. If your cap lacks a damper, install an inline backdraft damper in the duct run near the hood.

Ignoring makeup air. A 600 CFM or higher hood in a tightly sealed modern house creates enough negative pressure to pull combustion gases from a gas water heater or furnace back into the house through the flue. This is a carbon monoxide risk that can be life-threatening. If you hear a whooshing sound when you open an exterior door while the hood is running on high, you have a depressurization problem and need a makeup air solution.

Frequently Asked Questions

Do I Need a Permit to Install a Range Hood?

It depends on your jurisdiction and the scope of work. Replacing an existing hood with a similar model in the same location with existing ductwork typically does not require a permit. New duct penetrations through exterior walls, new electrical circuits, or hoods rated above 400 CFM (which trigger makeup air requirements) often do require a building or mechanical permit. Call your local building department before starting the project. The answer takes two minutes and avoids potential complications when selling the house, since unpermitted work can be flagged during a buyer's inspection.

Can I Vent Through the Roof Instead of the Wall?

Yes, but wall venting is preferred when possible. Roof venting requires a longer duct run, which adds friction and reduces performance. It also creates a roof penetration that must be properly flashed and sealed to prevent leaks, and it makes grease cleanup of the duct termination more difficult since you need to climb onto the roof. If you must vent through the roof, use a proper roof cap designed specifically for kitchen exhaust. Do not use a standard plumbing vent cap or an attic ventilator. Kitchen exhaust caps have screens and dampers rated for the grease and heat that cooking produces.

How Loud Should a Range Hood Be?

Hood noise is measured in sones. Under 3 sones on low speed is generally considered acceptable for open-plan kitchens where you might want to hold a conversation while cooking. Under 6 sones on high speed is tolerable for heavy cooking sessions. High-end hoods with external or inline blowers (mounted in the duct run or on the roof rather than inside the hood body) are the quietest option, often under 1 sone on low. When comparing hoods, check the sone rating at each speed setting, not just the maximum CFM number, which corresponds to the loudest setting. A hood that is quiet on low and tolerable on high will get used far more than a screaming hood that everyone avoids turning on.

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