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 Kitchen Exhaust Calculation - KitchenExhasut v1.15

kitchen hood exhaust ventilation software with built-in hood configurations



To take a glance at all pocketEngineer software and OS requirements, click Overview.

For Android OS, see aKitchenExhaust.


 KitchenExhaust software: design on the move 

KitchenExhaust is a commercial Kitchen Hood Exhaust calculation software designed for Windows PC.  It is specially engineered by a professional engineer for design mobility & quick calculations.

Aim: creating a mobile design environment (
ShowMe!) for the practising engineers & designers in today's mobile world.

Results: Instant solutions at your fingertips.



- calculate kitchen exhaust airflow rate for various built-in hood configurations in accordance to Singapore Standard SS 553 (formerly CP13)

- filter sizer

- louvre sizer
- built-in data & guides

- "save-to-file" function for printing
- mobile & independent program (no setup is required) for Windows PC

- in SI and IP units


 Software design features:practical. . . 


The software is designed to be user friendly and flexible with built-in guides and explanations. The built-in hood configurations for ease of calculations are:
island hood
> 1-side wall-mounted
> 2-side wall-mounted
> 3-side wall-mounted



 Methods: Calculating Exhaust AirFlow Rate. . . 


There are many methods available to calculate the required exhaust airflow rate, namely:

- Face Velocity Method

- Linear Extract

- Thermal Convection/Heat Load Method

- Appliance Power Input

- Air Changes


Every country has its own local code of practice to calculate the required exhaust airflow rate. The exhaust flowrate calculation presented in KitchenExhaust software is based on SS 553 (formerly CP13) (click "calculation explained" for details). SS 553 (formerly CP13) uses the Face Velocity Method. CIBSE and Australian Standard AS 1668.2 use the similar concept, but not exactly the same.


The governing parameters used in determining the exhaust flowrate are:

- capture / face velocity

- perimeter of hood (open sides)

- distance from stove top to hood bottom


Results can be saved to text file for editing & printing.


Comparisons between SS 553 (formerly CP13) and AS 1668.2 . . . 


The exhaust flowrate calculations of SS 553 (formerly CP13) vs AS 1668.2 are presented below:


SS 553 (formerly CP13)

AS 1668.2 

Q (m3/s) = [1.4 x Vel x Factor] x Perimeter x Height


Q = [0.294 to 0.42] x P x H

(based on Vel = 0.3 m/s)

Q (m3/s) = [Vel factor/1000] x Perimeter x Height 


Q = [0.15 to 0.75] x P x H




Understanding the Capture / Face Velocity Method in SS 553 (formerly CP 13)  . . . 


An important point to note is that in SS 553, the capture / face velocity is based on the vertical face area of hood open sides as illustrated in Sketch A. It is not based on the hood base area as shown in Sketch B. Therefore, the distance from stove top to hood bottom, i.e., H and the number of hood open sides will greatly affect the exhaust airflow required.


To account for the different type of cooking, a multiplying Factor is employed in SS 553 for simplicity in calculation. For heavy duty cooking, a Factor of 1 is used. For light and medium duty cooking, a Factor of 0.7 is applied. Indirectly, this can be translated to design face velocity varying from 0.21 m/s (for low/medium duty cooking) to 0.3 m/s for heavy duty cooking.


Sketch A - Capture / Face Velocity in SS 553

Sketch B



Did you know ? . . . 


SS 553 has a built-in safety factor of about 15% in the kitchen exhaust formula presented.


Duct Sizing. . . 

As a guide, the design velocity for kitchen exhaust duct is about 10 m/s (2000 FPM). For good air distribution throughout the entire kitchen hood area, it is good to have 2 discharge ducts from the top of the hood join the main exhaust duct if the hood length is greater than 3 m (10 ft.). 



 Grease Filter Sizing . . . 



The design and selection of grease filter plays an important role in the kitchen hood exhaust system. Baffle type grease filter is commonly used. The use of mesh type grease filter is no longer allowed as per NFPA code. The optimum operating velocity range for baffle grease filter is 0.8 - 1.5 m/s (150 - 300 FPM). The filter area required is determined by:


Filter area required = Exhaust flowrate / Filter face velocity


Too few grease filters will increase the filter cleaning frequency as well as increase the resistance to the airflow.


KitchenExhaust program provides a built-in tool for sizing of grease filter.




Calculation Example 1 (Exhaust Flowrate) . . . 


A Chinese restaurant requires a kitchen hood of size 2m (L) x 1m (W) to be installed over its cooking appliances (wok). The 0.9m-high gas cooking stove is located against a wall. The hood installation height is 2.1m from floor. Determine the exhaust fan capacity and duct size.


The following is the result printout from KitchenExhaust program:



Kitchen Hood Exhaust calculations


1-side (L) wall-mounted Hood ......
Hood size: L =2 m
Hood size: W =1 m
Velocity, Vel =0.3 m/s
Distance, H =1.2 m
Factor, F =1
Nos. of Hood =1
Exhaust/Hood =7,257.6 CMH
Total Exhaust =7,257.6 CMH    


The following duct sizing result is calculated using  Ductulator Plus program (to be purchased separately):


Ductulator (equal friction method) calculations


Retangular Duct sizing......
Friction loss rate =1.0 Pa/m
Duct roughness, e =0.09 mm
Air volume =7257.6 CMH
Duct height =300 mm
Duct width =1,000 mm

Duct velocity =6.73 m/s

(1) Flow area, A = 0.300 sq.m
(2) Hydraulic dia, Dh = 461.3 mm
(3) Reynolds nos, Re = 206,078
(4) Relative roughness, e/Dh = 0.000195
(5) Friction factor, ff = 0.016996
(friction factor solved by ColeBrook equation)    



Calculation Example 2 (Grease Filter Sizing) . . . 


Determine the grease filter area required for the kitchen hood exhaust flowrate in Example 1 above.


Grease Filter Sizing


Air quantity = 7257.6 CMH
Filter face velocity = 1.2 m/s
Filter area required = 1.68 m2


Filter Size Selection:

508mm x 635mm filter panel

Each filter area = 0.2671 m2

Nos. of filter required = 6.3 = 7





Price: USD 7.90


Download now:

product detail 


OS requirements: Windows XP, Vista, 7,  8, ...                                          


For Android phone OS, see                     


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 to SS 553 (CP 13)


  Kitchen Exhaust explained  




 built-in guide




Louvre Sizer



Filter Sizer