Range hoods and kitchen ventilation

Cooking puts more into the air than most people register while it is happening: grease particles from anything sauteed or fried, moisture from every pot that boils, combustion byproducts from a gas burner, and fine particulates that settle on cabinet tops and HVAC filters for months after the fact. A hood that moves real air out of the house, rather than just recirculating it past a filter, is one of the few kitchen decisions with a direct effect on air quality and on how long the cabinets, paint, and finishes stay clean.

Ducted versus recirculating

How each type works

A ducted hood pulls air from over the cooking surface and exhausts it outside the house through ductwork, taking grease, moisture, and combustion byproducts with it. A recirculating hood pulls air through a filter, usually a mix of grease and charcoal media, and returns it to the room. The filter catches some grease and some odor, but it does nothing for moisture and nothing for combustion products from a gas range, both of which stay in the house.

Ducted wins on performance in essentially every case where it is physically possible to run a duct to the exterior. Recirculating exists mainly for situations where routing a duct outside is genuinely impractical, an interior kitchen wall with no path to an exterior surface, or specific downdraft configurations. If the house allows for a duct run, use it.

Recirculating filters and maintenance

Whether a hood is ducted or recirculating, the grease filter needs regular cleaning, generally every one to three months of normal use, since a clogged filter chokes airflow no matter how strong the fan is rated. On a recirculating hood the charcoal filter that handles odor is a consumable that needs periodic replacement, typically every six months to a year depending on how much cooking runs through the kitchen, and it does not reset or clean like the grease filter does. Skipping this maintenance is the most common reason a recirculating hood that once seemed adequate starts to feel useless.

Sizing the hood to the cooking appliance

A hood should generally be at least as wide as the cooking surface below it, and going a few inches wider on each side improves capture, especially over a range with burners near the front edge. Mounting height matters too: too low crowds the cook and risks contact with tall pots, too high lets the rising plume spread out past the hood's capture area before it gets pulled in. Manufacturer guidance for a specific hood and range pairing should be the final word, but a range hood mounted meaningfully outside the appliance's own recommended height range rarely performs as advertised regardless of how much air the fan can move.

CFM, the airflow rating, should scale with the cooking appliance rather than being picked from a generic chart. For gas, a common rule of thumb ties CFM to the burner output in BTUs, roughly one CFM of exhaust for every 100 BTUs of total burner output, though manufacturers vary in exactly how they express this. For electric and induction cooktops, sizing is generally driven more directly by hood width and cooking intensity than by a BTU calculation, since there is no open flame contributing heat and combustion byproducts to the plume. A serious home cook running a high-output gas range needs meaningfully more CFM than someone running a standard electric cooktop, and the appliance spec sheet is the right starting point either way.

Duct design decides whether the CFM number means anything

Rigid duct, elbows, and termination

A hood's rated CFM is measured under ideal conditions with a short, straight duct. Real installations rarely look like that, and every departure from ideal costs airflow. Smooth-wall rigid duct, round rather than rectangular where possible, moves air far more efficiently than corrugated flexible duct, whose ridged interior surface creates drag along the entire run. A long flexible duct with a few tight bends can cut real-world airflow by half or more compared to the rated CFM on the box, which is why a hood that looks powerful on paper can still leave a kitchen smelling like last night's dinner.

Minimizing elbows and keeping the run as short and straight as the house allows matters more than almost any other duct decision. Where the duct passes through unconditioned space, an attic or an unheated section of the house, insulating the duct keeps warm, moist exhaust air from condensing inside the metal, which over time can lead to water staining or corrosion at the termination point. A roof termination generally provides the cleanest, shortest path in a lot of single-story layouts, while a wall termination is usually simpler and cheaper where the geometry allows it. Either way, the exterior cap should include a backdraft damper, a simple flap that keeps outside air, insects, and cold drafts from coming back in through the duct when the fan is off.

Noise and sones

Hood noise is rated in sones, a linear-feeling scale where doubling the sone number sounds roughly twice as loud. A hood running at 3 to 4 sones on its lower speeds is generally tolerable for daily use, while some higher-CFM hoods on their top speed climb well past that and get used less often as a result, which defeats the purpose of buying a powerful hood in the first place. Remote inline blowers, mounted in the duct run rather than inside the hood housing itself, are the standard way to get high CFM without high noise directly over the cook's head, at the cost of a more involved installation.

Makeup air: why a strong hood needs a way to breathe

A powerful exhaust fan pulls a lot of air out of the house, and that air has to be replaced from somewhere. In a leaky older house, it gets pulled in through gaps around windows, doors, and other small openings without much drama. In a newer, tightly sealed, well-insulated house, and this applies to more Fort Collins construction every year as building envelopes get tighter, there are not enough incidental gaps to replace that air, and the exhaust fan can end up fighting the house itself: struggling to move rated airflow, pulling combustion gases back down a water heater or furnace flue, or making exterior doors hard to open while it runs.

The International Residential Code, published by the International Code Council, addresses this in Section M1503, which requires a makeup air provision where the kitchen exhaust system is rated above a threshold, commonly cited at 400 CFM. Below that threshold, most jurisdictions do not require a dedicated makeup air system; above it, the code calls for a way to bring outside air back into the house to replace what the hood is removing. A makeup air system typically consists of a duct that draws outside air into the mechanical system or directly into the kitchen area, often with a motorized damper that opens automatically when the hood runs above a set speed, sometimes tied electrically to the hood's own controls.

Fort Collins adopts the International Code Council family with local amendments, and the current cycle brings the 2024 editions of the residential, mechanical, and fuel gas codes, effective from 1 April 2026. The specifics of what counts as a compliant makeup air path in a given house still come from the mechanical design rather than from a rule of thumb, and the contractor confirms them with the building department as part of the permit submission. The permits guide covers what else that submission involves. Anyone specifying a hood in the 600 to 1200 CFM range that professional and semi-professional ranges often call for should raise makeup air with the design and mechanical trades early, since retrofitting a makeup air path after walls are closed is considerably more disruptive than planning for it during rough-in. The permits guide has more on how mechanical permitting fits into the overall project.

Downdraft and island hoods

A downdraft vent, which rises out of the counter behind the cooktop and pulls air down and across rather than up, is popular for keeping sightlines open over an island, but it works against the physics of cooking: hot air and rising steam naturally want to go up, and a downdraft system is asking that plume to reverse direction before it escapes. Capture rates on downdraft systems are consistently lower than on an overhead hood, particularly for anything in a tall pot. An island or peninsula hood mounted overhead performs better than downdraft but still has to work harder than a wall-mounted hood, since there is no wall behind the cooking surface to help contain the rising plume on one side, which is one reason island hoods are frequently specified with a bit more width and CFM than an equivalent wall installation. Anyone planning a kitchen island with the cooktop built in should weigh this tradeoff against the layout goal before committing to downdraft.

Over-the-range microwaves as a compromise

An over-the-range microwave with a built-in exhaust fan is a common compromise in a smaller kitchen or a tighter budget, since it combines two appliances into one footprint. The tradeoff is real: the exhaust fan built into a microwave is meaningfully weaker than a dedicated hood, the mounting height is dictated by microwave ergonomics rather than by ventilation performance, and duct runs from this position are often more convoluted than a purpose-built hood location would allow. It is a reasonable choice for light cooking, but anyone who cooks with oil regularly or uses high heat often will notice the difference against a dedicated hood, and it is worth weighing that against the space it saves, particularly in a small kitchen remodel where every inch of wall space matters.

Where ventilation fits in the project

The duct run for a range hood is typically planned during design and installed during the rough-in phase described in the remodel timeline guide, alongside the rest of the mechanical and electrical work covered in the electrical guide. Getting the hood location, duct path, and makeup air question settled before framing closes up avoids the far more disruptive alternative of retrofitting a duct route later. For a full breakdown of what a ventilation upgrade adds to the budget, the cost guide and the cost calculator both cover mechanical line items, and general terms are defined in the glossary.