Calculation of air volume CFM (Cubic Feet per Minute)

For vacuuming smoke per table in grill shops There are principles of thinking that emphasize “Catching and venting smoke”

directly from each table which must be designed to be sufficient for the amount of smoke generated The basic principles are as follows:


1. General principles for thinking CFM per table.

Extraction of smoke from the grill (Using charcoal/gas/electricity) must use the amount of air that can suck out all the smoke.

in order not to spread into the store which generally use the range:

🔸 250–500 CFM connect stove/table
Depends on stove type, hood size, and usage.


2. Factor used to determine CFM per table.

Factor details
Hood size: Larger hood sizes require more CFM.
Hood position: hanging above the head vs. sucking under the table (downdraft) has different suction rates.
Stove type: Charcoal → more smoke, gas/electric → less smoke.
Usage frequency Heavy-duty tables should have a higher CFM.
Wind speed at the mouth of the hood (Capture Velocity) is generally 100–150 ft/min.


3. Basic calculation method (using a hood to cover the stove)

Basic formula:

CFM = Area of hood mouth (sq. ft.) × Required wind speed (feet/minute)

Example:
 • Hood size: 2 feet × 2.5 feet = 5 square feet.
 • Required air speed: 120 ft/min.

CFM = 5 × 120 = 600 CFM per table

If it's a hood that hangs over your head or has a cloth around the edge, just 300–400 CFM may be enough.


4. Suction system under the table (Downdraft System)
 • Use CFM approximately 200–350 per suction point.
 • The suction vent must be designed near the stove. and has suction power at specific points


5. In the case of designing a whole store system

If there is 20 table:
 • Use an average of 400 CFM per table.

400 × 20 = 8,000 CFM total

Must select the main exhaust fan (Exhaust Fan) that supports 8,000 CFM and designed the air duct so that the pressure does not drop


6. Caution
 • Don't forget the Fresh Air Supply system to balance the air being sucked out. Otherwise, the shop will be stuffy and have strong winds.
 • Use a Backward Centrifugal Fan for sucking smoke with good resistance from the pipe.

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