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At the risk of many people climbing all over me… I have always used a 3.25 x 10 boot inverted at the top of the wall to a 6″ round pipe. Then I purchase pre-insulated duct to the roof vent or gable vent depending on the situation. And no I am not talking about roof vents for the attic space but the type intended for this purpose. It reduces the volume a bit ( by about 1/3 ) but on a short run it has never caused a problem that I know of. Just try to be sure both ends in the attic are well sealed to keep that humid air outside where it belongs.
SteveM
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At the risk of many people climbing all over me... I have always used a 3.25 x 10 boot inverted at the top of the wall to a 6" round pipe. Then I purchase pre-insulated duct to the roof vent or gable vent depending on the situation. And no I am not talking about roof vents for the attic space but the type intended for this purpose. It reduces the volume a bit ( by about 1/3 ) but on a short run it has never caused a problem that I know of. Just try to be sure both ends in the attic are well sealed to keep that humid air outside where it belongs.
SteveM
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>I am installing a new range hood in my kitchen. It will be ducted through a cold air attic, terminating with a roof cap. Duct will be 3.25 x 10. Do I need to insulate this duct to prevent condensation. If so what type of insulation would you suggest? Any other tips would be welcome.
*Condensation will definitely be an issue -- say when boiling water on a cold January day -- be sure it has somewhere to drain to. Any fireproof insulation should be OK. i believe there are code requirements on the thickness of the metal and such.
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>Thanks for the info. I ran 3.25 x 10 to the roof cap. Taped the joints with foil tape. Wrapped the duct with R-6.7 foil covered, flame resistant fiberglass duct wrap. Then taped the wrap with the foil duct tape. Entire run is about 14 feet. I think I've covered the bases.