Kitchen Hood Calculator

DIN 18869NFPA 96
Calculator Input
Enter kitchen hood specifications
m²

Total area of the kitchen hood

Number of cooking appliances under the hood

Type of cooking determines exhaust requirements

m

Height of hood above cooking surface

m/s

Required capture velocity at hood

Frequently Asked Questions

Common questions about this calculator

Calculate based on hood face area and capture velocity: Q = A × V, where A is hood opening area (m²) and V is capture velocity (typically 0.25-0.5 m/s). For commercial kitchens, use 200-300 CFM per linear foot of hood length, or follow manufacturer specifications for specific cooking equipment heat loads.

Capture velocity is air velocity at the hood face needed to contain cooking effluent. Typical values: light duty (ovens, steamers) 0.25 m/s, medium duty (fryers, griddles) 0.35 m/s, heavy duty (charbroilers, woks) 0.5 m/s or higher. Insufficient velocity allows grease, smoke, and odors to escape.

Type I hoods handle grease-laden vapors from cooking equipment (fryers, griddles, ranges) and require grease filters, fire suppression, and listed exhaust ductwork. Type II hoods handle heat and moisture only (dishwashers, ovens) without grease—no fire suppression required, standard ductwork acceptable.

Makeup air should equal 85-100% of exhaust air to maintain slight negative pressure (prevents odors spreading). Supply approximately 80% as tempered makeup air (to prevent drafts) and allow 20% transfer from adjacent spaces. Makeup air unit should be sized to match hood exhaust capacity.

Type I hoods require UL 300 listed fire suppression systems (wet chemical for cooking equipment fires). System components include: detection/fusible links, wet chemical agent tank, nozzles covering cooking surfaces and hood plenum, gas/electric shutoff, and manual pull station. Inspect every 6 months, service annually.

Clean grease filters weekly for heavy-use kitchens, bi-weekly for moderate use. Replace disposable filters monthly. Hood and ductwork interior should be professionally cleaned based on usage: monthly (24-hour operations), quarterly (heavy use), semi-annually (moderate use). Document all cleaning for fire inspection compliance.

Learn More

Commercial kitchen exhaust hood systems are critical life-safety and environmental control systems capturing and removing heat, smoke, grease-laden vapors, and combustion products from cooking appliances. These systems protect building occupants from fire hazards, maintain acceptable indoor air quality, prevent grease accumulation in ductwork (which can ignite causing catastrophic fires), and provide thermal comfort for kitchen workers. Proper design, installation, and maintenance are mandated by International Mechanical Code (IMC) and NFPA 96 "Standard for Ventilation Control and Fire Protection of Commercial Cooking Operations."

Hood Classification and Types: Type I hoods serve grease-producing cooking appliances (ranges, griddles, broilers, fryers) and must include grease filters (baffle or mesh style), automatic fire suppression systems (UL 300 wet chemical systems), and stainless steel or black steel ductwork with continuous welded seams. Type II hoods serve non-grease-producing appliances generating only heat and moisture (steamers, dishwashers, pasta cookers), requiring no grease filters or fire suppression with galvanized steel ductwork acceptable. Misclassifying hoods (using Type II for grease-producing equipment) dramatically increases fire risk and violates codes.

Hood Configurations: Wall-mounted canopy hoods (most common and economical) attach to walls with appliances in line. Island canopy hoods suspend from ceiling over island cooking stations requiring 20-25% higher exhaust rates (thermal plumes less contained). Backshelf/proximity hoods mount very close to cooking surfaces (150-300mm above) using lower exhaust rates suitable for low-ceiling applications. Proper sizing requires overhanging appliances minimum 150mm (6 inches) on all open sides per NFPA 96—undersized hoods allow grease-laden vapors to escape, depositing grease on ceilings and walls.

Exhaust Flow Rate Determination: Three methodologies codified in IMC and ASHRAE 154: (1) Area method (IMC Table 507.2.2) specifies CFM/ft² based on appliance duty—light duty 200 CFM/ft² wall (300 island), medium duty 300 wall (400 island), heavy duty 400 wall (500 island), extra-heavy duty 550 wall (700 island). (2) Perimeter method calculates 150-250 CFM per linear foot of hood perimeter. (3) Heat input method uses 100-150 CFM per 10,000 BTU/hr for gas appliances. Area method most commonly used for code compliance and permits.

Makeup Air Requirements: IMC Section 508 requires makeup air for exhaust systems exceeding 400 CFM, with capacity equal to exhaust minus lesser of 10% exhaust or 300 CFM. Example: 5,000 CFM exhaust requires 4,700 CFM minimum makeup air. Insufficient makeup air causes difficulty opening doors (negative pressure >12.5 Pa), combustion appliance backdrafting (carbon monoxide hazard), inadequate hood performance (grease spillage), and uncontrolled infiltration. Makeup air provided via direct-fired units (adds moisture), indirect gas/electric units (conditioned air, higher efficiency), or transfer air from adjacent spaces. ASHRAE 90.1 encourages energy recovery achieving 35-55% energy recovery.

Fire Suppression and Grease Removal: UL-listed automatic fire suppression systems (UL 300 wet chemical) mandatory for Type I hoods per NFPA 96 Section 10, consisting of fusible link detection (79-82°C), pressurized agent storage (potassium carbonate/acetate), distribution piping and nozzles, manual pull stations, and automatic fuel shutoff. System requires one nozzle per appliance or per 1.2m hood length. Baffle grease filters (standard method) capture 70-80% grease at 200-300 FPM face velocity requiring regular cleaning (daily to weekly). Electrostatic precipitators achieve 85-95% grease removal efficiency, extending cleaning intervals from semi-annual to annual.

Energy Efficiency and Code Compliance: ASHRAE 90.1 Section 6.5.7 requires demand-controlled kitchen ventilation (DCKV) using variable-speed exhaust fans modulating based on cooking activity (temperature sensors, optical sensors, time-based controls), saving 30-50% fan energy. Additional strategies include transfer air from dining areas, energy recovery on makeup air, low-velocity displacement makeup air, and high-efficiency EC motor fans reducing consumption 20-40%. NFPA 96 Section 11 requires professional cleaning on schedules based on cooking volume (monthly for high-volume heavy-duty, quarterly moderate, semi-annually light). Cleaning removes accumulated grease (fire risk), with NFPA 96 requiring cleaning when accumulation exceeds 1.6mm.

Standards Reference: NFPA 96 governs commercial cooking ventilation control and fire protection. IMC Sections 507-508 specify hood classification, exhaust rates, and makeup air requirements. ASHRAE 154 provides ventilation design methodology. UL 300 establishes fire suppression system testing standards. ASHRAE 90.1 Section 6.5.7 mandates demand-controlled ventilation for energy efficiency.

Small Restaurant Kitchen - Single Hood Over Range

Size kitchen exhaust hood for small restaurant with single cooking line

1
Hood Area: 3.2 m²
2
Appliances: 2
3
Hood Type: Type I
4
Hood Height: 1.1 m
5
Makeup Air: Yes

Result

Required exhaust:
2,720 m³/h (1,600 CFM)

Calculations

  • •
    Hood area: 3.2 m² × 500 CFM/sq ft (medium-duty per IMC Table 507.2.2) = 1,600 CFM
  • •
    Converted to metric: 1,600 CFM = 2,720 m³/h

Equipment

  • •
    Exhaust fan: Greenheck CSP-20-120 (3,000 m³/h @ 300 Pa, 1.8 kW), upblast roof discharge
  • •
    Ductwork: 400mm diameter stainless steel 304, continuous weld per NFPA 96, 2% slope
  • •
    Makeup air: Greenheck GMS-30 (3,300 m³/h, 150 kW gas heating to 15°C)
  • •
    Grease filters: 8× baffle filters 400×500mm, stainless steel, 45° angle

Fire Suppression

  • •
    Ansul R-102 UL 300 system (8 nozzles)
  • •
    Fusible links 79°C, manual pull station
  • •
    Gas valve shutoff + appliance shutdown interlocks

Energy

  • •
    Fan: 1.8 kW, MAU heating: 150 kW × 0.25 load factor
  • •
    Annual: 164,250 kWh/year + 68,400 m³ gas/year

Maintenance

  • •
    Professional cleaning quarterly per NFPA 96
  • •
    Fire system inspection annually
  • •
    Filter cleaning every 2-3 days (heavy use)

Additional Notes

Per IMC and ASHRAE 154, kitchen hood exhaust rates: Type I (grease-producing): 200-500 CFM per linear foot depending on appliance duty (light/medium/heavy). Type II (heat/steam only): 150-300 CFM per linear foot. Capture velocity at hood face: 100-150 FPM. Include 10-20% makeup air shortfall factor. Size hood to overhang appliances 6" on sides, 12" on front.

Full-Service Restaurant - Multi-Hood System with Dedicated Makeup Air

Design complete kitchen exhaust system for full-service restaurant with multiple hoods and integrated makeup air

1
Hood Area: 16.5 m²
2
Number of Hoods: 3
3
Cooking Type: Heavy Duty
4
Hood Height: 1.2 m
5
Makeup Air: Yes

Result

Total exhaust:
13,000 m³/h (three-hood system with VFD control)

Calculations

  • •
    Main hood: 9.0 m² × 550 CFM/sq ft (heavy-duty) = 4,950 CFM (8,415 m³/h)
  • •
    Secondary: 4.8 m² × 350 CFM/sq ft (medium-duty) = 1,680 CFM (2,856 m³/h)
  • •
    Dishwasher: 2.7 m² × 300 CFM/sq ft (Type II) = 810 CFM (1,377 m³/h)
  • •
    Total: 12,648 m³/h → installed 13,000 m³/h

Exhaust Fans (VFD-controlled)

  • •
    Fan 1 (main): 8,500 m³/h @ 400 Pa, 5.5 kW
  • •
    Fan 2 (secondary): 3,000 m³/h @ 350 Pa, 2.2 kW
  • •
    Fan 3 (dishwasher): 1,500 m³/h @ 300 Pa, 1.1 kW
  • •
    VFD: 40% prep hours, 100% service hours

Ductwork

  • •
    Main: 500mm SS304 (9.3 m/s), secondary: 350mm (9.7 m/s), dishwasher: 300mm

Fire Suppression

  • •
    Ansul Piranha dual-agent (18 nozzles, dual pull stations)
  • •
    Interlocks: gas shutoff, exhaust on, MAU off

Makeup Air

  • •
    Two Greenheck MUA-40 (7,000 m³/h each = 14,000 m³/h, 105% of exhaust)
  • •
    Heating: 300 kW/unit, Cooling: 50 kW DX
  • •
    Energy recovery: 45% effectiveness glycol loop
  • •
    Distribution: Low sidewall diffusers (displacement strategy)

Controls

  • •
    BAS (Niagara/Johnson Controls) with time schedule + boost switches
  • •
    MAU interlocked to exhaust fans (prevents negative pressure)

Energy

  • •
    Fans: 33,384 kWh/year (VFD saves 35%)
  • •
    Heating: 158,760 m³ gas/year
  • •
    Cooling: 50,400 kWh/year
  • •
    Energy recovery payback: 0.74-2.8 years

Maintenance

  • •
    Semi-annual cleaning (main hood), annual (secondary)
  • •
    Fire system inspection annually

Additional Notes

Commercial kitchen ventilation per IMC requires Type I hoods over grease-producing equipment with grease filters, fire suppression, and adequate makeup air. Makeup air requirement: 80-100% of exhaust to prevent excessive building depressurization (<-0.02" w. c. ). Makeup air options: Dedicated units with heating/cooling, transfer air from dining, direct-fired units. Interlock: Makeup air fans start when exhaust operates. Balance system: Slight negative pressure in kitchen (5-10 Pa) prevents odors entering dining.

Hotel Convention Center Kitchen - High-Capacity Multi-Zone Type I/II System with Grease Extraction

Design comprehensive exhaust system for large hotel convention center kitchen with multiple cooking zones, electrostatic precipitators, sophisticated controls

1
Hood Area: 80.5 m²
2
Number of Hoods: 4
3
Cooking Type: Heavy Duty
4
Hood Height: 1.2 m
5
Makeup Air: Yes

Result

Total exhaust:
116,000 m³/h (four-zone system with ESP and N+1 redundancy)

Exhaust by Zone

  • •
    Zone 1 (Main production): 38.5 m² × 600 CFM/sq ft = 39,270 m³/h (heavy-duty)
  • •
    Zone 2 (Banquet): 15.4 m² × 300 CFM/sq ft = 7,854 m³/h (light-duty)
  • •
    Zone 3 (Baking): 12.8 m² × 350 CFM/sq ft = 7,613 m³/h (medium-duty)
  • •
    Zone 4 (Stewarding): 14.0 m² × 250 CFM/sq ft = 5,950 m³/h (Type II)

Exhaust Fans (8 total, VFD-controlled)

  • •
    Zone 1: 2× 20,000 m³/h @ 500 Pa, 15.0 kW each (N+1 redundant)
  • •
    Zones 2-4: 1× 8,000 m³/h @ 400 Pa, 6.0 kW each
  • •
    Total capacity: 128,000 m³/h (110% of required)
  • •
    Average 65% load factor, 50-100% VFD modulation

Electrostatic Precipitators (ESP)

  • •
    6× Airstream or Filta units, 85-95% grease removal
  • •
    Benefits: 10× less duct grease, 80-90% less odor, reduced fire risk
  • •
    Auto wash nightly, collection tank weekly pump-out (25-40 gal/week)

Ductwork

  • •
    Main: 800mm SS304 (13.8 m/s), secondary: 500mm (9.0-10.2 m/s)
  • •
    Continuous weld per NFPA 96, 2% slope, vertical risers
  • •
    Rooftop: 900mm stack extensions (12-15 m/s discharge)

Fire Suppression

  • •
    Kidde Monarch dual-agent (6 systems, 78 nozzles total)
  • •
    6 manual pull stations, fusible links 79°C
  • •
    Gas/electric interlock, exhaust remains on per NFPA 96

Makeup Air (N+1 redundant)

  • •
    3× Greenheck MUA-120 (40,000 m³/h each, 2 operating + 1 standby)
  • •
    Heating: 350 kW/unit (700 kW operating)
  • •
    Cooling: 70 kW DX/unit (140 kW operating)
  • •
    Energy recovery: 45% effectiveness glycol loop (dual parallel)
  • •
    42 low sidewall diffusers (displacement strategy)

Controls

  • •
    BAS (Siemens Desigo/Tridium Niagara)
  • •
    VFD linked to hotel event management system
  • •
    Pressure monitoring: -3 to -8 Pa (prevents odor migration)

Energy

  • •
    Fans: 253,043 kWh/year (VFD saves 35%, payback 1.6 years)
  • •
    Heating: 176,400 m³ gas/year
  • •
    Cooling: 86,400 kWh/year
  • •
    Energy recovery payback: 1.75 years
  • •
    ESP extends cleaning intervals (insurance premium reduction possible)

Additional Notes

Industrial/institutional kitchens per NFPA 96 require comprehensive fire protection: UL-listed hood with grease filters, automatic suppression system (wet chemical), manual pull stations, exhaust duct fire-rated with access panels every 20', grease removal system (ESP or water-wash). High-volume operations: Demand ventilation with VFD controls on exhaust fans, modulate based on cooking activity (IR sensors, temperature), saves 30-50% fan energy. Monitor hood capture effectiveness: smoke test verifies no spillage at design conditions.

ASHRAE 62.1 - Ventilation for Acceptable Indoor Air Quality

ASHRAE 62.1-2022 (2022)

ASHRAEstandard

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