Hanging and Sealing Range Duct


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Old 10-16-17, 06:36 AM
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Hanging and Sealing Range Duct

I will be hanging 7" round duct for range hood exhaust. (This is for a very basic range fan.) I've planned a good route with minimal turns. The horizontal lengths will run through a joist bay with 9" to 10" joists.

  1. When hanging the duct, should I hang it tight to the floor above, and tight to the joist it runs parallel to, or do I want to keep a gap between both to prevent vibration noise?
  2. What kind of hanger straps should I use?
  3. I think I have decided to seal with duct mastic instead of foil tape, when sealing with mastic, which seams (if any) should I support with mesh fiberglass tape (pipe to elbow, pipe to pipe joints, round pipe side seam)?
 
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Old 10-16-17, 10:39 AM
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1. I like to keep the duct away from everything. Partially for noise and also if there is a fire I want the hot steel duct away from anything flammable.

2. I use metal strapping.

3. I never use a mesh tape on ducts.
 
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Old 10-23-17, 05:56 PM
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This duct will connect to an OTR microwave that I haven't picked out yet. I have to use 7" round duct from the outside wall cap down into the cabinet above the microwave, and then I will probably need to transition to a 10 x 3.25 duct to connect to the microwave.

For the round duct that will run straight down through the cabinet, how close should I position the duct from the finished wall?

(I want to install everything except that last straight piece now, and then plan to cut and connect that last piece and the transition after I have installed the cabinet.)
 
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Old 10-24-17, 07:48 AM
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Do not run your exhaust duct until you have the microwave/vent. They are all slightly different and there is no "standard" way so it's best to match your duct up to the vent. Another reason is the assembly order for the duct. It's best to have the male ends slip down into the female. That way any condensation or grease running down the duct stays inside the duct. So, it's best to start at the bottom and stack on the duct sections as you work up.

If you must install duct now I would position it to the rear of the cabinet. I would leave some room to be flexible but they are usually at the very back of the vent.
 
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Old 10-24-17, 09:43 AM
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For the round duct that will run straight down through the cabinet, how close should I position the duct from the finished wall?
The round duct should be at the very back of the cabinet. I would say about 1 to 1-1/4" from the wall and centered in the cabinet.
The reason for standing it off the wall is so you do not need to cut the nailing/hanger board at the top rear of the cabinet, you want it intact.

All microwave hoods use 3.25 x 10 dampers, here's a link to the transition required:
https://www.homedepot.com/p/3-1-4-in...10X7/100126594
 
 

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