Professional ventilation is one of the many costs faced by a new cafe or restaurant. Without it, staff can't work in the kitchen, and the customer areas would be unbearable. 

A large canopy is needed above open flames (eg on a stove or grill) to extract the hot, greasy air and smoke. One may also be needed above a large dishwasher to remove steam, depending on the capacity. If the exhaust extraction is too powerful, it will suck up chilled air produced by the front of house air-conditioning. If it's too weak, heat and fumes from the kitchen will affect the air-quality of the front-of-house. In a good installation, air-conditioning techs will 'balance' the extraction by providing a source of make-up air directly into the kitchen.

Extraction systems and hoods get greasy and dirty very quickly, so proper cleaning is essential - for filter panels in the hood, and for the inside of the ductwork, which should be installed with inspection hatches. There's a lot to plan, install and maintain - seek professional advice early.