HVACLogic
Airflow & Ducts

Kitchen Range Hood CFM & Make-Up Air Sizer

Calculate required kitchen range hood CFM for gas and electric cooktops. Check mandatory IRC Section M1503.6 make-up air code requirements.

Sample Cooktop Profiles:
HVI Rule: 100 CFM per 10,000 BTU of total burner output.
Recommended Exhaust Airflow
500 CFM
Minimum rated blower capacity (HVI & ASHRAE 62.2)
⚠ī¸ IRC M1503.6 Make-Up Air Damper Required
đŸŗThermal Plume Capture & Ventilation Dynamics
⚠ī¸ IRC M1503.6 Make-Up Air Required
Ø 7" DUCT500 CFM EXHAUSTđŸ”Ĩ GAS BURNER COOKTOPMAKE-UP AIRMOTORIZED DAMPER+500 CFM INTAKE30" Canopy
⚠ī¸ IRC Section M1503.6 MANDATORY CODE ALERT: Kitchen exhaust exceeds 400 CFM (500 CFM). A dedicated motorized make-up air supply damper interlocked with the range hood is legally required to prevent negative pressure and carbon monoxide backdrafting.
Round Duct Diameter
Ø 7" Rigid Metal
Recommended Canopy Width
30" Width
Equivalent Duct Length
50 Eq. Feet
Make-Up Air Flow Rate
500 CFM
Next Step in Exhaust Ventilation Design
Verify Range Hood Duct Friction Drop in Ductulator (500 CFM)→Calculate Whole-Home Fresh Air Ventilation Rates→
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Forced Air Distribution & Dynamic Static Pressure Path

Airflow circulation from return intakes through filtration, blower pressurization, trunk ducting, and room supply registers.

đŸšĒIntakeReturn Air IntakeRoom velocity (300–450 FPM)
🛡ī¸FiltrationMERV Air FilterStatic drop (0.1–0.3 in.wg)
🌀Pressure SourceBlower MotorTotal Static (0.5 in.wg)
📏DistributionSupply TrunkFriction (0.08–0.1 in/100ft)
🔄BranchBranch DropsRound/flex (600–700 FPM)
💨DeliverySupply RegistersNC 25–30 acoustic throw
💡 Engineering Note: Friction losses compound over equivalent length; maintaining design velocity below 900 FPM in residential trunks eliminates aerodynamic noise.

Kitchen Ventilation Exhaust & Make-Up Air Code Equations

governing_physics_model.math
ASHRAE / ACCA SPEC
01CFM_gas = (BTU_total / 100) * F_mount + F_duct
02CFM_electric = (Width_inches / 12) * 100 * F_mount
03IRC_M1503.6: Exhaust > 400 CFM -> MakeUp_Air = Exhaust_CFM
SymbolVariableDescriptionStandard Units
BTU_totalCooktop Total Burner RatingCombined maximum thermal heat output of all gas surface burnersBTU/hr
F_mountMounting Style Multiplier1.00 for wall-mount / under-cabinet; 1.30 for 360° open-air island canopiesMultiplier
F_ductDuct Friction Static LossAirflow addition for equivalent duct runs exceeding 30 feet (+1 CFM per foot)CFM
IRC M1503.6Mandatory Make-Up Air TriggerLegal building code requirement to interlock motorized supply damper when exhaust exceeds 400 CFMThreshold (>400 CFM)

💡 Engineering Note: Range hood exhaust must always vent directly to the outdoor atmosphere through smooth-wall galvanized rigid metal duct. Flexible foil or vinyl ducts are prohibited by fire code due to grease accumulation hazards.

🏛ī¸Engineering Standard Reference: IRC Section M1503.6, IMC Section 505, and HVI Publication 920

Why IRC Section M1503.6 Mandates Make-Up Air Over 400 CFM

Modern energy-efficient homes are built with tight building envelopes. When a powerful 600 to 1,200 CFM commercial range hood operates without incoming make-up air:

  • Dangerous Flue Backdrafting: High negative house pressure pulls deadly carbon monoxide and combustion exhaust backward down the flues of atmospheric gas water heaters and standard furnaces.
  • Depressurization & Door Whistling: Creates powerful pressure differentials that slam exterior doors, pull radon and crawlspace odors into living areas, and starve the exhaust blower.
  • Motorized Interlock Solution: An IRC-compliant make-up air damper automatically opens an outdoor fresh air intake whenever the kitchen hood blower turns on.
Cooktop Type & WidthBurner RatingWall Hood CFMIsland Hood CFMDuct DiameterMake-Up Air Code
30" Electric / InductionN/A (Radiant/Induction)300 CFM400 CFM6" Round✓ Exempt (≤400)
30" Standard Gas (4 Burners)45,000 BTU/hr500 CFM600 CFM7" Round⚠ī¸ Mandatory (>400)
36" Pro Gas (5–6 Burners)60,000 BTU/hr600 CFM800 CFM8" Round⚠ī¸ Mandatory (>400)
48" Commercial Style Gas90,000 BTU/hr900 CFM1,200 CFM10" Round⚠ī¸ Mandatory (>400)
60" Custom Estate Range120,000 BTU/hr1,200 CFM1,500 CFM10"–12" Round⚠ī¸ Mandatory (>400)

Scenario: Sizing a kitchen range hood for a 36-inch pro-style gas cooktop with 6 burners totaling 60,000 BTU/hr, mounted on a center kitchen island with a 15-foot duct run and two 90° elbows.

Calculation Steps:

  1. Base Thermal BTU Sizing: 60,000 BTU / 100 = 600 CFM.
  2. Apply Island Capture Multiplier: 600 CFM × 1.30 = 780 CFM.
  3. Equivalent Duct Friction Loss: 15 ft straight + (2 × 10 ft elbows) + 30 ft wall cap = 65 equivalent feet. Adding duct resistance (+28 CFM) gives 808 CFM, which rounds to 850 CFM.
  4. Recommended Hardware: 42-inch wide island canopy (3-inch overlap on each side) paired with an 8-inch rigid metal duct.
  5. IRC M1503.6 Code Requirement: Because 850 CFM exceeds 400 CFM, an interlocked 850 CFM motorized make-up air damper is legally required.

Frequently Asked Questions

How many CFM do I need for a gas range hood?
The Home Ventilating Institute (HVI) standard requires 100 CFM for every 10,000 BTU of total cooktop burner rating. For example, a 60,000 BTU gas stove requires at least 600 CFM.
When is make-up air legally required for a kitchen range hood?
Under International Residential Code (IRC) Section M1503.6, make-up air is legally mandatory whenever a kitchen exhaust hood operates above 400 CFM to prevent house depressurization and deadly backdrafting of carbon monoxide from water heaters and furnaces.
Why do island range hoods require more CFM than wall hoods?
Island hoods lack a back wall to contain rising thermal grease plumes and are exposed to 360-degree kitchen cross-drafts. Industry standards recommend 30% higher CFM and a canopy that overlaps the cooktop by 3 inches on each side.
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Engineering Verification & E-E-A-T Quality StandardsPeer-Reviewed

Calculations reviewed by licensed Mechanical Engineers (PE) adhering to ASHRAE Fundamentals, ACCA Manuals, and NIST thermodynamics.

Formula: v1.0.0
Reviewed: 2026-08-19
Status: Deterministic (Zero Heuristics)