Sizing exhaust hoods - air volume flow and capture velocities - online exhaust hood calculator
Exhaust hoods are essential in kitchens, laboratories and many industrial application for removing
- hazardous substances
- polluting contaminants
In general, for an exhaust hood to be efficient
- the height - y - should not exceed 1.20 m (4 ft)
- the distance - x - should not be less than 1/3 y
- the capture velocity - v1 - should not be less than 0.15 - 0.20 m/s (30 - 40 ft/min)
Note! Potential hazardous and polluting applications requires special solutions. Always check local regulations.
The capture velocity - v1 - of the exhaust hood can be estimated with the empirical equation
v1 = q / 2 y2 c (1)
v1 = capture velocity (m/s)
q = air volume flow (m3/s)
y = distance between table and exhaust hood (m)
c = circumference of the hood (m)
(1) can be modified to calculate required air volume
q = 2 v1 y2 c (1a)
Example - Kitchen Exhaust Hood
Required air volume in a exhaust hood with circumference 3 m, 1.2 m above the stove, can be calculated like
q = 2 (0.2 m/s) (1.2 m2)2 (3 m)
= 1.7 m3/s
Note! The units don't match since the equation is empirical (a result of experiments).
Exhaust Hood Calculator
The air flow volume in the exhaust hood can be calculated below
Exhaust Hood with internal Plate
The efficiency of an exhaust hood can be improved by adding an internal plate.
The required air volume for an exhaust hood with a plate can in general be reduced to approximately 80% compared to an exhaust hood without a plate.
Exhaust Hood with Side Walls
The exhaust hood efficiency can be further improved by adding side walls.