Range Hood Sizing and Kitchen Ventilation Done Right

Why Ventilation Gets Skipped and Why It Matters

Range hoods are often chosen late, by appearance, after the cabinets and cooktop are settled. The fan’s capacity and, more importantly, the duct route become afterthoughts, and many kitchens end up with a hood that recirculates or a duct that is too small, too long or ends somewhere it should not.

Cooking produces heat, moisture, grease and combustion byproducts from gas burners, along with fine particles from searing and frying. Without ventilation, grease settles on cabinets and ceilings, moisture adds to indoor humidity, and odors spread through an open plan. A properly sized and ducted hood removes most of that at the source.

Ventilation belongs in the kitchen plan alongside appliances and layout, because the duct route affects cabinets, ceilings and even the choice of cooktop location. Appliances, plumbing, ventilation and lighting are all locked before rough-in in a step-by-step kitchen plan, and the hood belongs on that list.

CFM Sizing by Cooktop Type

Airflow is rated in cubic feet per minute, or CFM. The Home Ventilating Institute’s guidance ties it to the size and position of the cooktop:

• Wall-mounted hoods: about 100 CFM per linear foot of cooktop, so a 30-inch range suggests about 250 CFM and a 36-inch range about 300.
• Island hoods: about 150 CFM per linear foot, because air reaches an island from all sides and the plume is harder to capture.

The Florida Residential Code sets a lower minimum for kitchen exhaust, 100 CFM for intermittent operation, which is a floor rather than a target for serious cooking.

Gas vs Induction Loads

Gas cooktops add combustion products and more heat than induction, and high-output gas ranges produce large plumes. A common industry rule of thumb sizes hoods for gas ranges by burner output, roughly 1 CFM per 100 BTUs of total burner capacity, which leads to much larger fans on professional-style ranges. It is a rule of thumb, not a code requirement, and it quickly pushes a hood into makeup air territory.

Induction produces no combustion byproducts and less ambient heat, so smaller fans are usually adequate, though cooking itself still generates grease, steam and smoke. In either case, the hood’s capture ability, its width and depth, matters as much as its fan rating.

Ducted vs Ductless

Ducted hoods move air outdoors. They remove heat, moisture, grease and odors and are what the Florida Residential Code describes as the standard: range hoods discharge to the outdoors through a duct.

Ductless, or recirculating, hoods pass air through grease and charcoal filters and return it to the kitchen. They trap some grease and odor but do not remove heat or humidity. The Home Ventilating Institute states that non-ducted recirculating hoods provide no actual ventilation. The code allows listed ductless hoods installed per their instructions where other ventilation is provided, which makes them an option when ducting is truly impossible, such as some condo units, but not an equal alternative.

Duct Run, Diameter and Termination

The Florida Residential Code sets the basics for ducted range hoods: the duct must have a smooth interior, be airtight, have a backdraft damper, be independent of other exhaust systems and be made of galvanized steel, stainless steel or copper, with narrow exceptions for certain downdraft systems.

Beyond those rules, performance depends on the route:

• Diameter should match the hood’s outlet; reducing it cuts airflow and raises noise.
• Length reduces airflow; every foot of duct adds resistance.
• Elbows reduce airflow more than straight runs; fewer and gentler bends are better.
• Termination must be to the outdoors, through a wall or roof cap, never into an attic, soffit space or garage.

A hood’s rated CFM is measured under test conditions. A long, bent or undersized duct delivers much less, so planning the route with the layout, and choosing the cooktop location with the route in mind, protects performance.

Roof vs Soffit Termination

Roof caps and wall caps are the usual terminations. A roof cap works well when the kitchen is under an attic and a short vertical run is possible, but it adds a roof penetration that must be flashed properly. A wall cap works well on exterior walls, with a short horizontal run.

Soffit termination, venting through the underside of the roof overhang, is sometimes proposed because it avoids a roof penetration. The concern is that soffits often contain attic intake vents, and exhaust released there can be drawn back into the attic, bringing grease and moisture with it. Many building-science sources and manufacturers prefer wall or roof caps for kitchen exhaust. What is acceptable for a particular house is a question for the hood installer and the local building department.

Wall Cap Backdraft Dampers

The backdraft damper keeps outdoor air, insects and rain from coming in when the hood is off. Dampers can be in the hood, in the duct or in the wall or roof cap. They should open freely, close tightly and be accessible for cleaning, since grease can make them stick. In Florida, a damper that seals well also keeps humid outdoor air out of the kitchen.

Choosing a Hood Style

Hood style affects capture as much as looks:

• Under-cabinet hoods mount beneath a wall cabinet. They are compact and affordable, with the duct running through the cabinet above.
• Wall chimney hoods mount on the wall with a decorative chimney cover over the duct. They are often larger and more powerful.
• Inserts and liners fit inside a custom hood enclosure built to match the cabinets, giving a built-in look with a proper fan inside.
• Island hoods hang from the ceiling over a cooktop in an island and need more capacity for the same cooktop.
• Downdraft systems rise behind or sit beside the cooktop and pull air down; they suit islands where an overhead hood is not wanted, with lower capture.
• Over-the-range microwaves combine a microwave with a fan; they capture less than a dedicated hood.

The right choice depends on the cooktop, its location and the duct route, not only on the look of the kitchen.

Hood Lights and Controls

Most hoods include lights that illuminate the cooktop, often LED with more than one brightness level. Controls range from simple push buttons to variable speed, timers that keep the fan running after cooking, and sensors that adjust speed to heat. A delay-off timer is useful in humid kitchens, since it clears lingering moisture and odors after the burners are off.

Makeup Air Requirements

A hood that exhausts air creates slightly lower pressure in the house, and air has to come back in from somewhere. In tight houses, powerful hoods can pull air through unintended paths, including backdrafting from gas water heaters or fireplaces.

The Florida Residential Code requires exhaust hood systems capable of exhausting more than 400 CFM to be provided with makeup air at about the same rate. Florida’s version includes an exception for single-family homes: makeup air is not required for systems of 400 CFM or less, or for systems between 401 and 800 CFM where there are no gravity-vented appliances in the conditioned living space. Hoods above those levels, or homes with gravity-vented appliances inside, need a makeup air solution designed with the HVAC system. That is mechanical work handled with the permit for the hood.

Hood Height and Capture Area

Capture depends on geometry. A hood that is wider than the cooktop, commonly by a few inches on each side, and deep enough to cover the front burners captures much more of the rising plume than a narrow one. Mounting height matters too: too low interferes with cooking and sightlines, too high lets the plume spread before it reaches the hood. Manufacturers specify mounting heights for each model, often in a range above the cooktop, and those instructions govern installation.

Island hoods need to be larger than wall hoods for the same cooktop, because cross drafts from the room disperse the plume. Where the cooktop sits in an island, the hood’s size and duct route are part of laying out the island.

Noise Ratings and Sones

Hood noise is rated in sones, a unit of perceived loudness. Lower numbers are quieter. Manufacturers typically publish sone ratings at the highest and lowest fan speeds. A hood that is too loud tends not to be used, which defeats its purpose.

Ways to get quieter performance include a hood sized so it can run at moderate speed for most cooking, a duct that matches the outlet size, fewer elbows, and remote or inline blowers that place the motor away from the kitchen. ENERGY STAR certifies some ventilation fans for efficiency and noise limits, which can help when comparing models.

Humidity and Grease in Florida Kitchens

In a humid climate, cooking steam adds to a moisture load the air conditioning is already working to remove. A ducted hood that runs during and after cooking removes that moisture at the source. The same humidity makes grease more noticeable, as it combines with dust on cabinet tops and ceilings.

Ventilation choices for a Florida kitchen therefore favor ducted hoods sized for the cooktop, dampers that seal well, and filters cleaned on schedule. Where a new hood needs a new wall or roof penetration, a larger fan or makeup air, the work usually involves permits, and which kitchen work needs a permit explains how that fits with the other trades.

HomeGuide’s 2026 cost data puts installing a new range hood with an outlet and ductwork at roughly $650 to $2,100, with the hood itself ranging widely by type and size. The hood, the cooktop location and the duct route are best chosen together when a kitchen is being remodeled, with electrical connections and any makeup air system handled by the appropriate licensed trades. That is a national planning range, not a quote; the duct route, the roof or wall penetration, electrical work and any make-up air requirement decide the actual cost.