and may even contribute to hearing loss. Variable speed fans are generally noisier at higher speeds and different models may have different noise levels. Vented hoods are generally noisier but more effective than recirculating hoods. Noise levels are measured on dB(A) scale or in sones (in the U.S.). Most kitchen hoods produce 60-70 dB(A), while "quiet" models can go as low as 40 dB(A). Noise levels are generally given for the maximum speed, so it may be useful to compare noise levels at specific flow rates. The European Union standardizes the measurement of hood noise. Flow Hood air flow is measured in liters per second (L/s), cubic meters per second (m3/s), or cubic feet per minute (cfm). See also Fume hood Kitchen ventilation Smoke canopy References External links Article: "Oversized Kitchen Fans--An Exhausting Problem" by Bruce Manclark in Home Energy Magazine Online January/February 1999 Home appliances Air filters Kitchen Products introduced in 1937