Range Hood Makeup Air Code: 2026 Guide

You picked the range: six burners, 48 inches of stainless steel, the kind of cooking power that makes a kitchen feel serious. The range hood to match is rated at 900 CFM — and that is where the project gets complicated in a way no appliance showroom mentions. A hood that powerful does not just remove cooking smoke. It removes air, hundreds of cubic feet of it every minute, and your house has to replace that air from somewhere. Without a planned path for replacement air — makeup air — the hood will pull it down your furnace flue, your water heater vent, or your fireplace chimney, bringing carbon monoxide with it.

This is not a theoretical risk or a comfort footnote. It is a range hood makeup air code issue, a safety issue, and a performance issue: a starved hood cannot capture cooking pollutants properly either. This guide explains the range hood makeup air code — the 400-CFM rule in the International Residential Code — why makeup air matters for combustion safety, the system options from simple dampers to tempered units, realistic 2026 cost bands, and how to get it right with your contractor and your local inspector.

The physics your showroom never mentioned

A range hood is an exhaust fan with ambitions. A 600–1,200 CFM pro-style hood running at full speed evacuates the air of a typical kitchen in minutes — and a house is not a balloon that simply deflates. As the hood exhausts air, the house goes slightly negative relative to outdoors, and replacement air infiltrates through every available path: window frames, door gaps, electrical penetrations — and, critically, the flues of fuel-burning appliances.

This is depressurization, and its dangerous form is backdrafting: instead of combustion gases rising up the flue and out of the house, the negative pressure pulls them down the flue and into your living space. The gases in question include carbon monoxide — odorless, colorless, and lethal. The appliances at risk are the ones with natural-draft or atmospheric venting: older gas furnaces, standard gas water heaters, fireplaces, wood stoves. (Sealed-combustion, direct-vent, and power-vented appliances are far less vulnerable, which is why the code treats them differently.)

There is a performance dimension too. A hood starved of makeup air cannot develop its rated airflow — the harder it pulls against a sealed house, the less it actually moves — so the expensive 900-CFM hood captures cooking pollutants worse than a properly supplied 400-CFM hood would. You are paying for power you cannot use and creating a hazard in the process.

The range hood makeup air code: the 400-CFM rule

The International Residential Code addresses this directly. IRC Section M1503.6 (2021 edition) states that where one or more gas, liquid, or solid fuel-burning appliances — that are neither direct-vent nor mechanically drafted — are located within the dwelling’s air barrier, each exhaust system capable of exhausting more than 400 cubic feet per minute must be provided with makeup air at a rate approximately equal to the exhaust rate, either mechanically or passively.

Unpack that carefully, because the details matter:

• The 400-CFM threshold applies to the hood’s capability, not the speed you usually run it. A 900-CFM hood run on low is still a 900-CFM-capable exhaust system under the code.
• The fuel-burning appliance condition is the trigger. If every combustion appliance in the home is direct-vent or power-vented (sealed combustion), the IRC’s makeup air requirement for the hood does not apply in the same way — though performance and comfort reasons may still argue for it.
• “Approximately equal” means the makeup air system should roughly match the exhaust rate — not a cracked window, which is neither automatic nor reliable.
• Automatic operation is required in practice: the makeup air must be provided when the exhaust operates, typically via an interlocked damper that opens with the hood.

Verify your local code. Jurisdictions adopt different IRC editions with local amendments, and some — notably parts of California — layer additional energy-code requirements on top. Your building department and your permit application are the final authority, not this article and not the hood manufacturer’s brochure. Bring the question to the permit counter before you buy the hood.

Makeup air system options, from simple to sophisticated

There are three tiers of residential makeup air, and the right one depends on your hood size, climate, and how the house is built:

1. Interlocked passive damper

The simplest compliant approach: a motorized damper in a dedicated duct from outdoors to the kitchen (or an adjacent space), wired to open automatically when the hood runs. Outdoor air enters passively, driven by the negative pressure the hood creates. This satisfies the code for most residential hoods, costs the least, and has almost nothing to break. The trade-offs: the incoming air is untempered (a blast of cold air in a Minnesota January), unfiltered unless you add a filter grille, and passive flow depends on the pressure difference — long or restrictive duct runs reduce what actually arrives.

2. Powered (fan-assisted) makeup air

A small supply fan in the makeup air duct delivers a controlled airflow regardless of duct restrictions or house tightness, interlocked with the hood. Better for large hoods (900+ CFM), long duct runs, or very tight homes where passive flow under-delivers. Adds electrical work, fan noise to manage, and a control sequence to commission — but it guarantees the air actually shows up.

3. Tempered makeup air unit

A powered unit with heating (and sometimes cooling) that tempers the incoming air before it enters the house — the residential cousin of commercial makeup air units. This is the comfort answer for cold climates with big hoods: no icy drafts across the kitchen while you sear steaks in February. It is also the most expensive option by a wide margin, needs a heating source (electric or hydronic), and is frankly overkill for a 500-CFM hood in a mild climate.

Option	Best for	Comfort	Complexity
Interlocked passive damper	Hoods 400–600 CFM, mild climates, budget projects	Untempered air; noticeable in winter	Low — damper, duct, interlock wiring
Powered makeup air	Hoods 600–1,200 CFM, tight homes, long duct runs	Untempered unless heated; reliable airflow	Medium — fan, controls, electrical
Tempered unit	Large hoods in cold climates, luxury builds	Best — heated incoming air	High — heater, controls, commissioning

2026 cost bands

Makeup air is one of those costs that surprises buyers because it was never in the appliance budget. Planning ranges for 2026:

• Interlocked passive damper system: roughly $300–$900 installed — the damper kit itself, a duct run to an exterior wall or roof, and the electrical interlock to the hood. Straightforward when planned during a remodel; more when retrofitted through finished walls.
• Powered makeup air: roughly $1,200–$2,500 installed, depending on fan size, ductwork, and electrical.
• Tempered residential unit: roughly $2,500–$6,000+ installed, driven by the heating component and controls. Commercial-grade tempered units run far higher and are rarely appropriate for homes.

Costs are 2026 US market ranges; get itemized local quotes. Note that the hood project itself — a pro-style hood runs $650–$2,500+ installed before ductwork — plus the makeup air system together define the real budget. Price them as one project.

One cost-saving reality check: if your home’s combustion appliances are all direct-vent or power-vented, confirm with your code official whether the makeup air requirement applies at all — and even if it does not strictly apply, weigh the hood-performance and comfort case before skipping it. Conversely, do not try to dodge the requirement by buying a 399-CFM hood for a 48-inch pro range: an undersized hood over a high-output range captures poorly, which defeats the purpose of the range you bought.

Design details that separate good installs from code-minimum ones

Where the makeup air enters matters. Dumping untempered air directly behind the cook will fight the hood’s capture — the incoming airstream can push cooking plumes away from the hood. Better practice: introduce makeup air low and away from the range (a toe-kick grille, a transfer grille to an adjacent room, or a floor register), letting it wash across the kitchen toward the hood. Your HVAC contractor should be thinking about this; if they are not, find one who is.

Filtration deserves a mention: outdoor air is not clean air. A simple filter grille on the intake keeps pollen, dust, and insects out of your kitchen — a small addition that separates thoughtful work from minimum-code work. In wildfire-prone regions, consider how the intake behaves during smoke events (a damper you can manually close, plus a plan to not run the big hood on the worst days).

And the interlock must actually work: the damper or fan should activate with the hood automatically, not via a separate switch you will forget. Test it at final inspection — hood on, damper open; hood off, damper closed. This is a five-minute verification that catches the most common installation failure.

Commission the system, don’t just switch it on. After installation, verify the makeup-air damper actually opens when the hood runs — interlocked dampers can be wired backward — and confirm the relief path works. The thorough version is a worst-case depressurization check: all exhaust fans on, air handler running, interior doors closed, then measure pressure at the water heater or furnace draft hood with a manometer. If the house pulls past roughly -5 Pascals with fuel-burning appliances inside the air barrier, something needs adjustment. Ask whether commissioning is included in the quote; a contractor who looks confused is telling you something.

And a final practical note: label the system. A small printed label on the damper and the control — “makeup air interlock, do not disconnect” — prevents a future homeowner, handyman, or even you in three years from “fixing” a damper that seems stuck open. Combustion safety equipment that gets disabled by accident is worse than none at all, because it creates false confidence.

Permits, inspections, and hiring

A pro-style hood with makeup air is a permitted project in most jurisdictions: mechanical permit for the exhaust and makeup air ductwork, electrical permit for the hood circuit and interlock wiring. The inspector will want to see the interlock function and the damper operation. Pull the permits — unpermitted kitchen exhaust work is exactly what a buyer’s home inspector flags, and rework after the fact costs multiples.

Hire a licensed HVAC/mechanical contractor for the makeup air design and installation, coordinated with whoever installs the hood. Ask: “How many interlocked makeup air systems have you installed for hoods over 400 CFM?” and “How do you verify the airflow actually matches the hood’s exhaust?” The contractor should be able to describe the sizing method, not just the damper brand. If your home has atmospheric-vented combustion appliances, mention it explicitly and ask how the design protects against backdrafting — the answer should reference depressurization, not just code compliance.

Next steps

Before you buy the hood: confirm your local code edition and amendments with the building department; inventory your combustion appliances (atmospheric vs. direct-vent vs. power-vented); size the hood to the range honestly; and get the makeup air system quoted as part of the same project, not as an afterthought. A great range deserves a hood that can actually breathe — and a house that stays safe while it does. Costs are 2026 US market ranges; get itemized local quotes.

Frequently asked questions