Cubic Feet per minute (CFM) is a measure of the volume of air being exhausted through your range hood. This measurement is always based on when the hood is running at full speed and at zero pressure

Suggested CFM Requirments

Electric

Generally speaking an electric cook top is low powered and should only need a range hood output between 150cfm - 300cfm. If you have an electric deep fat fryer you will need to treat it as if it was a gas stove top.

Gas

"Regular" gas cook tops have outputs of up to around 40,000btu [British Thermal Units] and, since they are almost always used in an "against the wall" situation, you can use this simple formula to help make your choice. Calculate your cook top's btu rating by adding the power of each burner and then divide the total by 100, e.g. a 30,000btu top will require a 300cfm fan.

Outside / Ducted - The polluted air rises, is pulled up by a fan, passes through filters, and is exhausted outdoors through a metal duct. High BTU gas cooking equipment should always be ducted to the outside of the home.

Inside / Non-Ducted - A fan draws the polluted air through filters and then recirculates the cleaned air back into the kitchen. Non-vented hoods circulate the air through charcoal or other filters fitted in the house and then let out purified air for recirculation.

Ducted or Vented hoods

Aluminum Mesh Filters - Designed to trap grease before the smoke and odors are forced outside. Filters require periodic cleaning and many are dishwasher safe.

Metal Baffle Filters - Designed to force fumes and steam to suddenly change direction, the grease then separates from the air and filtered air passes into the range hood.

Non-Ducted or Non-Vented hoods

Charcoal Filters - Designed to trap grease and other smaller molecules so they don't blow back into the kitchen. These charcoal filters aren't washable but need to be replaced every few months