Range Hood Makeup Air Requirements: The 2026 Guide to the 400 CFM Rule
Hood-winked.
Is your range hood working against your home? Discover the critical rules for balanced kitchen ventilation.
In modern construction, we prioritize a "tight" building envelope to maximize energy efficiency. By using air sealing and insulation, advanced house wraps, and high-quality windows, we’ve successfully minimized the energy loss found in older, leakier homes. However, this increased airtightness changes the physics of how a home "breathes"—particularly when we introduce high-capacity exhaust systems like pro-style range hoods.
While a high-CFM range hood is excellent for managing cooking odors and grease, in a high-performance home, it can inadvertently create a pressure imbalance. To keep your home healthy and your air quality high, it is essential to understand the logistics of air exchange and the "400 CFM threshold."
The Science of Negative Pressure
Airflow in a home is a zero-sum game: Air out must equal air in.
In a sealed home, if a range hood is exhausting 800 or 1,000 Cubic Feet of air per Minute (CFM), that air must be replaced immediately. Because the home is airtight, the exhaust fan creates a vacuum (negative pressure). To satisfy this vacuum, the home begins to pull replacement air—often called "infiltration air"—from the path of least resistance.
The Humidity Factor
In the South, the air being pulled into the home through light fixtures, baseboards, and wall cavities is often heavily saturated with moisture. When this warm, humid air meets the backside of cool, air-conditioned drywall, it can reach its dew point. This creates hidden condensation within the wall assembly, which can lead to long-term indoor air quality issues and mold growth that often go unnoticed until they become significant problems.
Safety and the Combustion Appliance Zone (CAZ)
The most critical technical concern with negative pressure is its impact on the Combustion Appliance Zone (CAZ). Gas-fired appliances, such as natural-draft water heaters or furnaces, rely on the buoyancy of hot exhaust gases to rise through a flue and exit the home.
A powerful range hood is a mechanical force that can easily overcome this natural draft. If the house is too tight, the hood can pull combustion gases—including carbon monoxide—back down the flue and into the living space. This is known as backdrafting, and it is the primary reason building codes have become more stringent regarding makeup air.
Consumer Planning Guide: Calculating Your Home's Needs
Where to Find Your Stove’s Requirements
You generally won't find a "Required CFM" label on the stove itself. To find the exact manufacturer recommendation:
Check the Installation Manual: Look for the "Ventilation Requirements" section. Manufacturers often specify a minimum CFM and a recommended height for the hood above the cooking surface.
Locate the BTU Rating: On gas stoves, there is usually a metal tag (often under the burners or inside the broiler drawer) that lists the BTU rating for each burner. You will need to add these together for the "BTU Rule" calculation.
Search the Model Number: If you’ve lost the manual, search the model number on the manufacturer's website and look for the "Product Specifications" or "Technical Data" sheet.
1. Calculate Your Required CFM
Before selecting a hood, calculate the minimum power your cooking surface requires. Choosing the right fan power depends entirely on what you are cooking with and where it sits in your kitchen. Follow the calculation guide below that matches your setup.
Electric & Induction Cooktops
Electric and induction cooktops produce heat, but they don't produce combustion byproducts like carbon monoxide. The primary goal here is managing steam, grease, and odors. The standard calculation is 100 CFM for every 10 inches of stove width.
| Electric Cooktop Width | Wall-Mounted (Min CFM) | Island-Mounted (Min CFM) | Pro Tip |
|---|---|---|---|
| 30" Range | 250 - 300 CFM | 375 - 450 CFM | Island hoods need more "reach" for capture. |
| 36" Range | 300 - 450 CFM | 550 - 600 CFM | Cross-drafts significantly reduce efficiency. |
| 48" Range | 800 - 1,000 CFM | 1,200 - 1,500 CFM | High-performance cooking requires high-volume air. |
Gas Ranges (The BTU Method)
Gas ranges are more demanding because they release heat and moisture into the air along with combustion gases. To stay safe and keep your kitchen cool, you must calculate based on the total thermal output of your burners. The rule is 100 CFM for every 10,000 BTUs.
| Total Burner BTUs | Minimum CFM Required | Makeup Air Required? | Pro Tip |
|---|---|---|---|
| 30,000 BTUs | 300 CFM | No | Standard for most entry-level gas ranges. |
| 45,000 BTUs | 450 CFM | YES | Exceeds the 400 CFM safety threshold. |
| 60,000 BTUs | 600 CFM | YES | Typical for mid-range pro-style cooktops. |
| 90,000+ BTUs | 900+ CFM | YES | Heated Makeup Air is recommended in SC. |
Island Hoods (The "Open Air" Factor)
Because an island hood sits in the middle of the room, it is vulnerable to "cross-drafts"—air moving when people walk by or when the HVAC kicks on. Without a back wall to help funnel smoke upward, you need a higher velocity of air to ensure pollutants don't escape into your living space. For any island installation, increase your calculated CFM by 50% to account for the lack of a wall.
2. The "400 CFM" Makeup Air Threshold
Most building codes require a Makeup Air (MUA) system if your hood exceeds 400 CFM.
The 400 CFM Rule: This is the tipping point where a home can no longer "leak" enough air to keep up with the fan. Crossing this threshold without a dedicated intake puts your home at risk for negative pressure.
Pro Tip: Many high-end hoods now feature Airflow Control Technology (ACT), which allows a technician to calibrate the blower to a specific CFM limit to meet local codes. Most of these hoods are Energy Star compliant.
3. Understanding Noise (Sones)
Unlike decibels, Sones measure how the human ear perceives sound. Use these levels to ensure your ventilation remains usable:
1–2 Sones: Whisper quiet. Similar to the hum of a high-end refrigerator.
3–4 Sones: Comfortable. About the level of a normal office conversation.
5–6 Sones: Loud. Similar to a vacuum cleaner; usually reserved for high-heat searing.
7–10 Sones: Very Loud. Comparable to a lawnmower; can be intrusive for long periods.
Understanding Range Hood Noise: Sones vs. Everyday Sounds
Installation Best Practices: Where the Air Goes
Proper termination is just as important as fan power. If the air isn't leaving the building envelope entirely, you are simply moving the moisture to a different part of the structure.
Avoid Recirculating Hoods: These "ductless" units catch some grease but do zero to remove heat, moisture, or combustion gases.
Termination: All exhaust must vent directly outdoors—never into an attic or crawlspace. Dumping hot, humid air into a dark attic is a guaranteed recipe for mold and structural rot. For roof terminations, follow the 3-2-10 Rule: The vent should be at least 3 feet high, and at least 2 feet higher than any part of the roof within a 10-foot horizontal radius to ensure proper drafting and prevent moisture re-entry.
Rigid vs. Flex Ducting: Always use rigid galvanized steel. Flexible "slinky" ducting has ridges that trap flammable grease and create friction that kills fan performance.
The Slope Factor: Horizontal runs should have a slight pitch toward the exterior to ensure any condensation drains outside rather than dripping back onto your stove.
The Solution: Make-Up Air (MUA)
A proper MUA system uses a motorized damper that opens automatically when the hood is turned on. It provides a "clean" path for fresh air to enter, preventing the vacuum effect, stopping moisture from being sucked through your walls, and protecting your CAZ from backdrafting.
How to Tell if You Have a Pressure Problem
The Heavy Door Test: Turn your range hood on high. If your front door is hard to pull open or feels "sucked" into the frame, you have a pressure imbalance.
The Tissue Test: Hold a single ply of toilet paper near an electrical outlet on an exterior wall. If it flutters toward you, your house is "breathing" through the walls.
Test & Know
If your home feels "clammy" when you cook, or if you are planning a major kitchen upgrade, don't guess—measure. Rappid Energy specializes in the complex physics of modern homes. We use specialized tools like Blower Doors and Manometers to measure exactly how your home reacts to your exhaust fans. We ensure your luxury kitchen remains a source of comfort, not a source of moisture or safety concerns.
For Informational Purposes Only: This guide is not a substitute for professional engineering or legal advice. Always defer to your manufacturer’s installation instructions and the specific building codes of your local jurisdiction, as requirements vary by region. Rappid Energy and the author assume no liability for safety hazards or code violations resulting from installations performed without professional onsite diagnostic testing and certified mechanical oversight.