Microwaves

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.

Wattage

A higher wattage will cook foods faster. Most microwaves have power that falls between 600 to 1200 watts. Recipes written for the microwave usually specify power of at least 800 watts so the foods cook evenly.