NOTE: Any listed and labeled
RATE OF EXHAUST FLOW CALCULATIONS
Based on the 1996 International Mechanical Code.
The Rate of air flow required for a vent hood is calculated using the following definitions (Fig. 6):
Q= Rate of Air Flow in Cubic Feet Per Minute or [ CFM ] Required for the Hood.
A = Area of Hood Opening in Feet2 = (L x W)
D= Clearance Height = Distance in Feet from lower lip of hood to top of dishwasher chamber.
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CLEARANCE | ➤ | LENGTH | ➤ | ||
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HEIGHT |
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P = Perimeter of Hood that is Open. This |
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depends on the hood design, as follows: |
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| Fig. 6 | |||||
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| Perimeter Calculation Formula |
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| Hood Design |
| Corner | Wall | Island | ||||
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| Number of Open Sides |
| 2 Sides Open | 3 Sides Open | 4 Sides Open | ||||
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| P = |
| L + W | L + W + W | L + L + W + W | ||||
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| Dimensions |
| Feet | Feet | Feet | ||||
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If there are four open sides (Island Design), the calculation of the Rate is as follows:
Q = 75 x A
If there are three or fewer open sides, the calculation of the Rate is as follows:
Q = 50 x A
As an alternate method, the Rate can be calculated as follows:
Q = 50 x P x D
Example:
L = 3 | W = 3 | D = 2 |
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| Rate Calculations |
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| Hood Design | Corner | Wall | Island | |
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| Number of Open Sides | 2 Sides Open | 3 Sides Open | 4 Sides Open | |
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| Q = 75 x A |
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| 675 CFM | |
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| Q = 50 x A | 450 CFM | 450 CFM |
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| Q = 50 x P x D | 600 CFM | 900 CFM | 1200 CFM | |
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