The Exhaust Hood & Makeup Air Sizing Tool helps commercial kitchen designers and HVAC professionals calculate the required exhaust CFM for their hood system and the corresponding makeup air needs. By inputting hood type and linear length, this tool applies NFPA 96 and ASHRAE guidelines to ensure proper ventilation, fire safety, and worker comfort.
How It Works
Core Formulas:
Exhaust CFM = Hood Length (ft) × Duty Factor (CFM/ft)
Makeup Air (MUA) CFM = Total Exhaust CFM × MUA Percentage
Net Exhaust = Total Exhaust CFM - MUA CFMDuty Factors by Cooking Type
| Duty Type | CFM/ft | Typical Equipment |
|---|---|---|
| Light Duty | 150 CFM/ft | Ovens, Steamers, Kettles |
| Medium Duty | 300 CFM/ft | Range, Fryer, Griddle |
| Heavy Duty | 450 CFM/ft | Charbroiler, Wok, Salamander |
Makeup Air Fundamentals
Makeup air replaces the air exhausted by the hood system. It is typically designed at 80-90% of exhaust volume to maintain a slight negative pressure in the kitchen. The remaining 10-20% is drawn from adjacent spaces as transfer air.
FAQ
Q: Why is makeup air necessary for my kitchen?
A: Makeup air replaces the air exhausted by the hood system. Without it, the kitchen would experience negative pressure, causing backdrafting and occupant comfort issues.
Q: What’s the difference between Type I and Type II hoods?
A: Type I hoods handle grease-laden vapors from cooking. Type II handles heat, steam, and odors only. This calculator is intended for Type I hoods.
Q: How much CFM do I need for a 10-foot hood?
A: For medium-duty cooking (range/fryer), 10 ft × 300 CFM/ft = 3,000 CFM minimum exhaust.
References
- NFPA 96: Standard for Ventilation Control and Fire Protection of Commercial Cooking Operations
- ASHRAE Standard 154: Ventilation for Commercial Cooking Operations
- International Mechanical Code (IMC) — Chapter 5: Exhaust Systems
- Local building and fire codes