The purpose of a kitchen extractor fan is to distillate odours, moisture, air and grease while cooking. Each state has their own specific extractor fan regulations, but there are also some general statewide regulations.
An extractor fan in a residential kitchen should have the capability to replace air in the kitchen every hour between 10 and 15 times.
For an extractor fan to have an effect it must be of a certain size. This size is regulated by the British Thermal Unit (BTU) capacity of your stove. If your stove has a BTU of 10,000, the extractor fan is required to change the air at a rate of 100 cubic feet per minute.
For optimal performance, the kitchen extractor fan ducts are required to be short in length and as straight in positioning as possible. The brackets and supports for the ducts should be comprisesd of non-combustible material.