Kitchen Exhaust Fan Types and Considerations

Kitchen exhaust fans capture the grease, steam, and smoke while you're cooking. Without an exhaust fan, these particles build up and leave a filmy coat of slime on your kitchen counters, walls, floors, and furnishings. Exhaust fans are also necessary in eliminating smoky haze that drifts throughout your home every time you cook (that possibly sets off your fire alarms.)

Types of fans

• Ranges with built-in exhaust fans. Most ranges come with a built-in exhaust fan, but these fans don't do anything to improve the quality of your breathing air. All they do is pull the steam and smoke up from the stovetop and circulate it through the vents making it easier to see, but it does not remove the smoke or smelly odors.

• Overhead/kitchen hood exhaust fans. The exhaust fan is tucked up under a decorative hood and is available with multiple speeds. This is the most popular (and logical) method because it takes advantage of the fact that "hot air rises;" thus, the air naturally wants to flow upward into the dome. Overhead fans can suck up air and smoke much more effectively than a downdraft and overheads can save space while the downdrafts can't.

• Downdraft exhaust fans. These are easier to install, clean, maintain, and dispose of. Though less effective than overheads, if you don't require a huge capacity then the downdraft type of exhaust fan could be a good choice for you.

The three biggest errors

• The fan installed is not powerful enough for the size of the kitchen.

• The installer did not vent it properly.

• The need for makeup air was overlooked.

Size matters

• Ranges come in various sizes and with various BTU ratings. Exhaust fans come in various sizes and with various CFM ratings (cubic feet per minute.) CFM is a measure of how much air the fan will circulate. For every 10,000 BTU's produced by your range your exhaust fan needs to have a CFM rating of 100. So, assuming you are using your fan with a range hood, all you need to know as you're shopping for your fan is how many BTU's your range has. For example, if your range measures 30,000 BTU's, then you'll need a fan that is rated for at least 300 CFM.

• Another way to size your kitchen exhaust fan is to measure the square footage of the kitchen floor and multiply that number by two to arrive at the cubic feet per minute of output for the fan. Example, if your kitchen is 300 square feet you would need a fan that would exhaust at least 600 CFM of air flow.

Where to vent

• There are kitchen fans that vent into the attic space, but this is never a good choice due to the potential fire hazard risk. If you accidentally start a fire on your stovetop the ductwork will pull the fire into your attic and cause a much bigger fire. The best choice possible is to vent up through the roof to the outside of your house.

Safety precautions

• Since the fan is connected to metal ductwork that leads from the fan to the roof of your home, each joint in the ductwork should be carefully taped with special metal-foil duct tape.  It is important that no air seeps from the duct to other parts of the house because that air is full of grease and wherever it lands in your home would pose a significant fire hazard.  

• Make-up air vents are crucial to your health – what goes out must come in. Make-up air is the air that replaces the air that has been exhausted. Kitchen exhaust fans have an appetite for air. Sucking a lot of air out of a house can cause back drafting if a make-up air inlet is not installed. Back drafting can and will cause carbon monoxide to be drawn back down a chimney or a metal vent pipe, and smoke (or smoke odors) from fireplaces. Be extra cautious with new construction – the homes are built specifically to keep outside air from entering the home and the tighter the home the worse the problem. In order for your home to replace the air that has been exhausted it will look for any opening to the outside. Installing an exhaust fan without make-up air is not only dangerous, the less makeup air available, the harder the fan must work.

• Have a vent pipe to the outside installed with an electrically controlled damper. This will add a bit to the cost but you'll feel safer in the long run. When the kitchen exhaust fan is turned on the electrically controlled damper opens and allows makeup air to enter your home.

Aside from kitchen fans

• If you're really into clean air, in conjunction with your kitchen exhaust fan, install a house-wide exhaust system. There is one motorized fan for the entire house and when you turn it on the air from each room with a suction duct is sucked out – kind of like a vacuum cleaner. Works great if you fry a lot of food, have pets, or if you have very athletic kids – keeps the odors where they belong, out of your home!

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