Range and Cooktop Hoods
Range and cooktop hoods work because warm air rises. The canopy, or hood, portion of the system, usually made of steel, should be at least as wide as the range top to effectively capture the air and steam as they rise (see "Sizing a Ventilation System"). The hollow cavity, or sump, under the hood collects the dirty air until a fan pulls or pushes it through the ducts to the outside. A deep sump holds more air than a shallow one. But because of the demand for sleeker hoods, manufacturers have come up with different ways to handle the air. Some have made their fans more powerful, but others, including Broan-NuTone and Gaggenau, have introduced hoods that pump air out around their edges, creating a flow that traps the air from the cooking surface until the fan can remove it. At the heart of the ventilation system is the fan(s) it uses. An axial fan looks like a ceiling fan, while a centrifugal fan resembles a squirrel cage. A centrifugal fan moves more air than an axial unit does, and is better suited to long duct runs. However, an axial fans is less expensive. The amount of air the fan can move is measured in cubic feet per minute (cfm). The Home Ventilating Institute recommends a minimum of 40 cfm for every linear foot of your range. That means a 120-cfm unit should be just enough for an average-size range. For a downdraft unit, that figure jumps to a minimum of 150 cfm. A remote-mounted motor, whose fan is located at the end of the ductwork rather than in the canopy so it's less noisy, also requires a higher cfm. How much higher depends on a number of variables, with length and layout of duct runs being the most important. Figure up to 400 cfm for a wall unit and as high as 600 cfm for an island cooktop. "You'll get much better results with a stronger ventilating system" Dale Rammien says. That's especially true if you have a commercial range, which can throw out upwards of 15,000 Btu per burner. That means a tremendous amount of extra heat and more gaseous by-products. "A commercial range requires a souped-up hood," Rammien adds. In addition to a powerful fan, a quality system will also come equipped with sturdy filters. These trap grease and particles and prevent them from passing into the ductwork, clogging it and turning it into a potential source of fire. The filter should fit snugly and lift out easily for cleaning. The Noise Factor
Manufacturer research shows that noisy homeowners do not use their fan if it's noisy. A few years ago, most systems operated at between 3 and 8 sones. Some now run at less than 1 sone -- about equivalent to the gentle hum of a refrigerator. Generally speaking, the stronger the unit, the noisier it is when running. But much depends on the quality and location of the motor, the type of fan, the type of the filter and the size and length of the ductwork.

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