From: Neon John <johngdNOSPAM@bellsouth.net> Subject: Re: Restaurant Kitchen Vent Noise Date: Sat, 04 Dec 1999 21:18:38 EST Newsgroups: sci.engr.heat-vent-ac,alt.sci.physics.acoustics Owning a restaurant or two, I thought I'd throw my 2.5 cents worth (inflation) in. My experience with exhaust fans is that they are not very noisy unless a) they are out of balance from grease buildup and/or b) they have bad bearings. I high volume restaurant can build up enough gunk on the fan to cause noise in a week or so. Very few independent restaurant owners/managers deal with this problem until something breaks or the fan quits working. Bearing noise is common because the major brands of fans use ordinary ball bearings to support the vertical fan shaft (belt drive). These are not designed to handle the thrust and quickly become noisy preliminary to failure. I've solved that problem with my fans by installing Timken tapered bearings on my fans. Five+ years and no noise or failure. Second comment. I don't have my NFPA standard at hand at the moment but in general, the fan is NOT required to be welded to the duct. The hood and duct is required to be welded or otherwise attached together in an approved manner. The fan typically just sits on the grease gutter. This allows the fan to easily be dismounted for cleaning. It is certainly possible to isolate the fan from the duct if that becomes necessary. In reply to the UK writer, the reason the code requires the duct to be so secure is that the grease can build up an inch thick or more in a poorly maintained duct and when that catches on fire and the fire is driven by the high velocity air going to the fan, the heat is intense enough to melt (not just distort) thin ductwork. As an ex-volunteer fireman, I've seen just how quickly a grease hood fire can torch a building. While generally opposed to mandatory building codes, this is one area where I think the NFPA standard is a little lax. I have a foot clearance between my hood vent pipes and anything flammable. I stopped at a foot only because major structural changes would have been required to go further. The ducts are insulated with high temperature insulation. John -- John De Armond johngdSPAMNOT@bellsouth.net http://neonjohn.4mg.com Neon John's Custom Neon Cleveland, TN "Bendin' Glass 'n Passin' Gas" |