In order to work out the correct airflow requirements for your commercial kitchen you will need to add up the airflow values from the table below.

Common gas equipment                       m3/sec

4 burner gas range                                    0.23

6 burner gas range                                    0.338

single gas fryer                                          0.15

double gas fryer                                         0.29

Large gas Salamander Grille                     0.225

Gas combi oven (stand mounted 6 grid)   0.29

Electric equipment

4 ring electric cooker                                  0.13

6 ring electric cooker                                  0.2

twin electric fryer                                        0.22

single electric fryer                                     0.15

elec. combi oven  (stand mounted 6 grid)  0.25

Finally you need to multiply the airflow figure by a canopy factor. This allows for having open ended, or walls or island type canopies.

Wall mounted with wall to one end                x1.2

Wall mounted with walls to both ends           x1.15

Wall mounted open both ends                      x1.25 

Island canopy, wall one end                         x1.25

Island canopy, wall both ends                      x1.15

Island canopy, no walls                                x1.35

This will give the required extract figure which can be used to specify your kitchen extract system. It's a good idea to allow an extra 10% or more as a safety factor.