Quieting stove exhaust fan

We have an over the range microwave with built in exhaust that vents outside through the attic. It is noisy as heck and I want to quiet it. Seems like most of the noise is coming from the front grill where the fan would exhaust back into the room if I did not have the outside vent. Some noise is also coming from the cabinets directly above the microwave as the rectangular metal duct goes directly up through it and into the ceiling.
I have access to some 1" thick very dense fiberglass insulation used in the marine industry for thermal insulation. I am thinking of gluing this onto the outside edges of the metal duct as well and stuffing it inside the space in the microwave behind the grill. It won't cost anything to try, but was wondering if there is anything better that is readily available at the local home depot.
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On Tue, 23 Oct 2007 11:58:33 -0700, snipped-for-privacy@hboi.edu wrote:

I used to have an over-the-range microwave and the fan did not move much air. After 15 years of use I was glad the microwave died. I replaced it with a model that has 5 speeds and you can program it to run the fan for a selected number of minutes and shut off. If I want a quiet fan I set it to "1." If I want to quickly vent I set it to "5." It has a fan that is 3X more powerful. Whatever you use to insulate, use something that is non-flammable.
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The noise is probably a function of that brand of fan. Some are quieter than others and you just have to listen to different models or, more doeable, do some online research. If there isn't and money for a change out then I would use a little of that foam to make some stand-offs to get the fan away from the cabinets. I would put a 2" x 2" piece under each corner at the very least. That should eliminate your cabinet vibration. Best of luck to you!
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C & E wrote:

I had a range hood above the upper oven of a 2 oven range that was very noisy. Bad thing #2 is that it was a recirculation type. I gutted it, fan and filter, left the grease filter screen, and added an on-roof fan. After cutting a hole in the top of the hood and connecting it to the fan unit, all was pretty quiet. I later remodeled, replacing the double oven with a cook top and a new hood. I connected it to the same fan.
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I'd cover the insulation with aluminum duct tape to seal the edges and keep it from absorbing grease and becoming a fire hazard.
Bob
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The amount of noise from the fan is measured in SONE - a 1.5 sone is very quiet - a 7 sone microwave (most GE over-the-range microwaves) is very loud. The noise comes from the style of fan blade, it's speed and type of motor. A mocrowave fan 'may' have a hard time over coming the static pressure of trying to push air up a long duct to the roof - esp if the duct is the cooragated stuff or has any 90 angles. Go to Lowe's and go to the plumbing section and look for bathroom exhause fans - there should be a Broan (sp) display with three fans - from loud to quiet. This will give an example of sone ratings. Maybe remove the fan from the microwave and install an in-line quiet fan in the duct somewhere in the attic area with a switch next to the microwave. The fan being in the attic will move any fan noise from the kitchen to the attic. Keep the existing grease filter in the microwave though.
Probably very little use to ask a sales person which microwave has the most quiet fan as they usually say something like "the more expensive the unit, the quieter it will be".
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