Range hood venting: where the air has to go

Why does a range hood need to vent outdoors?

Because the pollutants a stove makes stay in the house unless something pushes them out. The EPA's page on nitrogen dioxide and indoor air quality lists gas stoves among the main indoor sources of the gas and recommends using an exhaust fan that is vented to the outdoors. A recirculating hood can catch grease and some odor in its filter, but it returns the air, and whatever gases are in it, to the same kitchen.

Cooking on any fuel also puts moisture, heat, smoke and grease into the air. Moisture that never leaves ends up on window glass, inside cabinets and in the paint above the range. So even in an all-electric kitchen, a hood that moves air outside does work a filter alone cannot.

Everything else here follows from that: the question is rarely whether to vent outside, and more often how to get a duct from the hood to an outside wall or the roof by a route that works.

What the residential code says about hood exhaust

The International Residential Code (IRC) is the model code most U.S. cities build their residential rules from. We quote it here second-hand, as it appears in the National Kitchen & Bath Association's Kitchen Planning Guidelines, which reprint the code points next to the association's own advice. Your city adopts its own edition and can amend it, so treat these as the common baseline and ask the local building department about your address.

As NKBA reports it, the IRC asks for three things from a kitchen hood:

• At least 100 cfm of exhaust. Cfm means cubic feet per minute, the volume of air the fan moves.
• A duct that ends outdoors. The exhaust is not allowed to stop in an attic, a soffit or a crawlspace.
• Makeup air for a hood system rated over 400 cfm. Above that size, air has to be brought back into the house to replace what the hood removes.

Why the attic, soffit and crawlspace are ruled out

Each of those spaces is inside the building shell even though it feels like the outdoors. Warm, wet, greasy air dumped into an attic condenses on cold framing and roof sheathing, and the grease builds up where nobody cleans it. A soffit vent sits right under the eave, close to the attic intake vents, so the air can be drawn straight back in. A crawlspace traps moisture under the floor. The rule is plain on purpose: the duct runs to a cap on an outside wall or the roof.

What makeup air means in practice

A hood can only push out as much air as the house lets back in. In a tight, newer home, a large fan with nowhere to draw from may move far less than its label says, and it can pull air backward through other openings, including the flues of gas appliances. Makeup air is a planned path for replacement air, often a duct with a damper that opens when the hood runs. If you are drawn to a large hood, this is the point where it changes from an appliance swap into a mechanical design question, and the code threshold NKBA quotes is 400 cfm.

How much airflow do I need?

Begin with NKBA's recommendation, then size up only for a reason. The association's guidelines recommend a ducted hood of at least 150 cfm. That is a trade recommendation, not code; it sits above the 100 cfm code floor quoted above and well under the 400 cfm point where makeup air comes in.

A few things push the right number one way or the other:

• The cooktop's fuel and size. A gas range makes combustion gases as well as cooking fumes, which is why EPA ties its advice to gas stoves in particular.
• The hood's shape and position. A hood mounted against a wall captures more of the rising plume than one floating over an island, where cross drafts carry smoke sideways.
• The duct. Long runs, many elbows and a duct narrower than the hood's outlet all cut the air a fan actually moves. A smaller fan on a short, straight duct can outperform a bigger fan on a poor one.
• How you cook. Frequent searing and frying produce more smoke than steaming and simmering.

Ask the contractor what airflow the hood will deliver on the duct route planned for it, not only what the box says. If the number you want is above 400 cfm, ask in the same breath how makeup air will be handled.

California's kitchen exhaust rules

In California, kitchen ventilation is also part of the state Energy Code. Energy Code Ace, the California Energy Commission's training and reference resource, summarizes the 2025 single-family mandatory features in its page on Section 150.0 mandatory features and devices. Under §150.0(o), every kitchen needs local mechanical exhaust; in an open kitchen, that exhaust has to be demand-controlled; and the hood has to be a rated product whose performance is verified in the field.

Field verification means someone checks the installed system, not just the model number on a spec sheet. That is a good reason to keep the hood's documentation and choose the model before the cabinets above it are ordered, so the inspection is not a surprise.

What one Bay Area city's handout adds

Cities often publish short checklists that turn the codes into plain steps. The City of Pleasanton's residential kitchen alteration handout (revised January 2023, based on the 2022 California codes) says kitchen exhaust must go outdoors and include a backdraft device, a damper that lets air out but closes when the fan is off, so outside air and pests do not come in through the duct. Your own city's handout may differ in detail, so read the one for your address, but Pleasanton's is a clear picture of what a California inspector looks for.

For the wider California picture, including lighting, outlets and the order of the work, see the kitchen remodeling A to Z.

Does switching to induction change the venting plan?

It changes the reasons, not the need. The federal efficiency label program says induction can be upwards of three times as efficient as gas, and the U.S. Department of Energy writes that induction is up to three times as efficient as gas and up to 10 percent more than smooth-top electric. An induction cooktop burns no fuel, so it adds no combustion gases to the room.

Food still smokes, steams and spatters on induction, though, so a hood vented outdoors still earns its place. What does change is the rest of the job: going from gas to induction usually means a new electrical circuit and dealing with the old gas line, which brings in an electrician and possibly a plumber. Plan the hood and the range together, since they share a wall, a budget conversation and often a permit.

Planning the duct route before anything else

The hood you can have is usually decided by the path its duct can take. Before choosing a model, look at where the range sits and work out where a duct could go:

1. Straight through the outside wall when the range is on an exterior wall. This is often the shortest route.
2. Up through the cabinets and the roof when there is no exterior wall behind the range. The duct passes through the attic but must not end there; it continues to a roof cap.
3. Through a floor or ceiling joist bay to an outside wall, which can work for an island but needs care with joist direction and length.

Whichever route it takes, the duct should end at a proper cap with a backdraft damper, sized to the hood's outlet. If the plan moves the range, it moves the duct too, so settle the layout first. Our small kitchen remodel guide walks through layout decisions in order, and the home renovation checklist puts the hood in the wider sequence of work.

Older homes have one more step. If cutting a new duct opening means disturbing painted walls or ceilings in a house built before 1978, EPA's lead rule may apply; our guide to a lead-safe kitchen remodel explains when.

What to tell the contractor when you send a request

Three facts let a contractor understand a hood job quickly. Put them in your request and the first conversation can be about your kitchen instead of basic questions:

• The hood type. Wall-mounted, under-cabinet, island, a microwave-hood combination or a downdraft unit, and whether the current one is ducted or recirculating.
• The duct route. Whether the range sits on an outside wall, whether there is an attic or another floor above, and where the current duct, if any, comes out.
• The range fuel. Gas, electric or induction now, and whether you plan to switch.

When you talk to contractors, ask what airflow the hood will deliver on that route, whether makeup air will be needed, and whether the work needs a permit in your city. Our list of questions to ask a contractor covers the rest, and in California you can check a contractor's license on CSLB's site and read what a home improvement contract has to include. In Dallas–Fort Worth, see our guide to a kitchen remodel in Dallas–Fort Worth.

Where Contractor Near Me fits in

Contractor Near Me is a free request service for the San Francisco Bay Area and Dallas–Fort Worth. We are not a contractor, we hold no contractor's license, and we do not install hoods, run ducts or do any of the work. You tell us about the project, and we call or email you back about it. For the full scope of a kitchen job, see kitchen remodeling, more guides on the blog, or contact us.

Sources: U.S. EPA, Nitrogen Dioxide's Impact on Indoor Air Quality (official), NKBA, Kitchen Planning Guidelines (trade recommendations; IRC points quoted second-hand), Energy Code Ace, 2025 Section 150.0 Mandatory Features and Devices, Single-Family (official), City of Pleasanton, Residential Kitchen Alteration handout, rev. January 2023 (official), Federal efficiency label program, reasons to switch to electric cooking (official), U.S. Department of Energy, Making the Switch to Induction Stoves or Cooktops (official).