Typically, the hood must extend beyond the cooking equipment: on all open sides for a canopy style hood and on the ends for a back shelf style system. In a typical situation, if a hood system is not capturing and containing the effluent from the cooking process, it will spill in the front corners of the hood.

The movement of people can involve moving an object of sufficient size and speed to create secondary air currents which pirate effluent from the cooking process. While the effect of one individual is only momentary, it can be a problem if the traffic occurs continually.

Opening windows in the kitchen creates draughts and also affects the ideal shape of the thermal plume. It can be one of the most difficult problems to solve.

Experience has shown that such air draughts can have a much greater effective throw distance to produce a greater detrimental effect on the capture envelope than one would normally expect.

Overhang

All canopy type kitchen ventilation requires front and end overhangs. In most instances, extending the overhang of a hood system from the typical 300 mm will help insure capture and containment in most kitchen settings. Recommended height from the floor to the lower edge of the canopy is 2000 mm.

When two hoods are used in double island installation, the pair of hoods negates the need for a rear overhang. The need for a front overhang remains. Canopies require some distance of overhang on each end of canopy.