Kitchen cooktops produce water vapor, particulates, atomized grease and cooking odors. Gas cooktops also give off carbon dioxide, nitrogen dioxide, carbon monoxide and nitrous oxide as combustion by-products. A vented hood over a cooktop is the best way to safely direct contaminants out of your kitchen and into the outside air. The International Residential Code mandates minimum ventilation rates that have been adopted by many local and state jurisdictions to ensure homeowner safety. Checking the codes for your area is highly recommended.
Range Hood Location
For optimal performance, standard range hoods should project at least 20 inches from the back wall and be mounted no more than 24 inches above the cooktop. The hoods should be at least as wide as the cooking surface and rectangular in shape, rather than angled, so that combustion and cooking by-products may be captured effectively and quickly directed out of your home. Smaller vents that are incorrectly mounted increase the risk of backdraft that can contribute to indoor air pollution.
The 2003 International Residential Code mandates a minimum ventilation rate of 100 cubic feet per minute for wall-mounted hoods. This rate increases in the presence of open grilling or other cooking that generates excessive amounts of steam or smoke. High-output cooktops should be vented at a rate of 1 cubic foot per minute for every 100 British Thermal Units (BTUs) of heat output. Kitchen island hoods, mounted at a minimum of 27 inches above the cooktop, require a minimum ventilation rate of 150 cubic feet per minute.
Some cooktops substitute downdraft fans for overhead vent hoods. These fans are either flush-mounted or located at the back of the cooktop as a pop-up that reaches approximately 8 inches above the cooktop surface. Downdraft fans provide ventilation rates between 400 and 600 cubic feet per minute and are sufficient for indoor cooktop barbecues, grills and pots smaller than 3 inches in height. Taller pots require overhead range hoods to effectively capture water vapor and cooking contaminants.
Updraft Vent Hood Options
Updraft vent hoods located over a cooktop may be one of two types. The first pulls polluted air upward, passes it through air filters in the hood then vents the air outside through a metal air duct. The second updraft vent hood option draws the contaminated air upward, feeds it through a system of filters then returns the cleaned air into the kitchen. Outdoor- vented hoods require placement on an exterior wall to allow for venting through the roof. Air return vents are suitable for kitchens where external venting is not possible.
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