Soak the range hood’s metal grease filter in a mixture of hot water, dish soap, and baking soda, then clean it with a soft brush. In a kitchen where frying is frequent, do this every 2 to 3 weeks; in a kitchen where frying is infrequent, do it once a month. A grease-saturated filter reduces suction and becomes a layer of fuel that can ignite if a flame rises from the stove.
Steam rising during cooking carries tiny suspended droplets of grease. A range hood’s metal filter is designed to catch these droplets, and a thin layer of grease builds up on it after every frying session and every sauté. Over time, the layer thickens, clogs the openings, and keeps the hood from drawing in steam and odors from the kitchen even when it is running at the same speed. When heated, accumulated grease can also drip from the filter and leave sticky marks on the stove. Keeping the filter clean also protects the range hood motor.
The main danger is fire. Grease that builds up in the filter is flammable; when oil flares up in a pan and flames rise from the stove, the grease-saturated filter can catch fire, and the fire can spread inside the range hood and from there to the cabinets. A clean filter greatly reduces this risk. A high flame rising from the stove can also reach the filter. For the same reason, never leave a pot unattended while working with hot oil under the range hood. If a small grease fire starts in a pan, slide the lid over the pan, turn off the burner, and do not move the pan; leave the lid on until the pan has cooled. If the flames grow or reach the range hood, leave the house and call 112.
To clean it, remove the filter from the range hood and place it in the sink or a large basin. Pour in enough very hot water to cover it, then add a few drops of dish soap and 2 to 3 tablespoons of baking soda. Leave the filter in this mixture for 15–30 minutes; the grease softens and begins to loosen from the openings. Then scrub both sides with a soft brush and rinse with hot water. Repeat the process a second time if the filter is very dirty.
Do not reinstall the filter until it is completely dry. Do not use strong alkaline cleaners or washing soda on an aluminum filter for extended periods; these substances darken and dull aluminum. Filters approved by the manufacturer can also be washed in the dishwasher, but an aluminum filter may change color over time in the machine. Wipe the inside surface of the range hood and the filter frame with a damp cloth as well, because grease builds up around the filter, too. When cleaning is finished, hold the filter up to the light; if light passes evenly through the openings, all the grease has been removed.
Some range hoods also have a carbon filter behind the metal filter. This filter captures odors, not grease, and must not be washed; water makes it unusable. Depending on how heavily it is used, a carbon filter is generally replaced every three to six months; the product manual gives the exact interval. Range hoods that vent air outdoors do not have a carbon filter, only a metal filter. Marking the metal filter’s cleaning day on a calendar helps you remember. If a sticky layer of grease remains on your finger when you touch the filter, it is already well past time to clean it.