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The illustration shows a typical commercial kitchen application utilizing a roof mount upblast exhaust fan in conjunction with a supply fan. Read on to determine how to size your exhaust and supply fans.
Designed to exhaust contaminated air in commercial and industrial application.
For commercial kitchen applications, when not specified by code, the following guidelines may be used to determine the minimum kitchen hood exhaust CFM:
|Type of Cooking Equipment||CFM/Ft.2 of Hood|
|Light Duty||Oven, Range, Kettle||50|
|Medium Duty||Fryer, Griddle||70|
|Heavy Duty||Char broiler, Electric Broiler||100|
Static pressure usually ranges from .625"(15.9mm) to 1.0" (23.4mm) for 1 story buildings.
*NOTE - Some local codes required 100 CFM/Ft.² of hood area for wall style hoods.
Supply air is recommended to be 90% of your determined exhaust CFM. The remaining 10% will be drawn from adjacent areas to the kitchen, which helps prevent undesirable odors from drifting into areas such as the dining room.
The pressure generated by fans in ductwork is very small. Yet, accurately estimating the static pressure is critical to proper fan selection. Fan static pressure is measured in inches of water gauge. One pound per square inch is equivalent to 27.7 in. of water gauge. Static pressure in fan systems are typically less than 2 in. of water gauge, or 0.072 Psi.
The amount of static pressure that the fan must overcome depends on the air velocity in the ductwork, the number of duct turns (and other resistive elements), and the duct length. For properly designed systems with sufficient make-up air, the guidelines in the table can be used for estimating static pressure.
Static Pressure Guidelines
|Non-Ducted:||0.05 inches to 0.20 inches|
|Ducted:||0.2 inches to 0.4 inches per 100 feet of duct (assuming duct air velocity falls within 1,000-1,800 feet per minute)|
|Fittings:||0.08 inches per fitting (elbow, register, grille, damper, etc.)|
|Important: Static pressure requirements are significantly affected by the amount of make-up air supplied to an area. Insufficient make-up air will increase static pressure and reduce the amount of air that will be exhausted. Remember, for each cubic foot of air exhausted, one cubic foot of air must be supplied.|