Author Topic: Going from a 4" duct to 8" used in a range hood insulation question.  (Read 1701 times)

Offline Huck50

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Hi:
 New member here and looks like a good place to ask questions...anyways,we are re-doing our kitchen and the 'old' under cabinet 30" 250c.f.m 4" ducted range hood is going to go,being replaced with much stronger variable speed 750 c.f.m.,with rotary control 30"wall mounted unit. This new unit comes in either a 6 or 8 inch exhaust duct opening..I am choosing the 8" version.
My question is about insulating the ducting section that goes pretty well straight up through the attic,maybe a 12 feet section to the roof.Since this ducting(8") will be much larger than the existing 4" and with the more powerful blower,I am concerned about condensation building up inside the duct and running back down into the new hood and new dual-fuel range.
Should this 12 foot section that goes through the attic be insulated,as it gets pretty cold here in Canada during the winters?
Also where should the back-draft damper be installed (at the roof portion)?
Thanks,Huck50 :-\

Offline Admin

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Re: Going from a 4" duct to 8" used in a range hood insulation question.
« Reply #1 on: July 10, 2017, 07:39:44 AM »
Yes, the duct must be insulated with RSI 0.5 (R4.2).

Quote
9.32.3.10. Ducts - (3) Where an exhaust duct passes through or is adjacent to unheated space, the duct shall be insulated to not less than RSI 0.5.

The roof jack vent must be equipped with a damper.  The new fan should also have a damper installed at its exhaust port.

Quote
9.32.3.12. Outdoor Intake and Exhaust - (9) Except for exhaust outlets serving heat recovery ventilators, exhaust outlets shall incorporate backdraft dampers.

Offline Huck50

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Re: Going from a 4" duct to 8" used in a range hood insulation question.
« Reply #2 on: July 10, 2017, 02:27:48 PM »
Sorry...what do those numbers (RSI 0.5 (R4.2) mean?
 Are you saying I should have two back-draft dampers?
 Lastly,if I may...what is the difference between the "roof jack vent" and the goose neck vent I was going to go with...just the looks? Thanks,Huck50

*EDIT* After some searching,I found out that RSI is the Metric measurement and R is the Imperial measurement.
I still can't find the difference between a roof jack vent and a goose neck vent or when you would use one over the other..they both look different?! Thanks,Huck50

Offline Huck50

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I looked,but I can't find anything related to this topic: 'Maximum c.f.m limit of range hood blowers without necessitating the use of a make-up air unit.'...in Ontario,Canada.
I plan to buy a range hood with a variable speed and a maximum of 750c.f.m. and my house is pretty air tight,so I don't want any problems,by creating a vacuum when using the gas range with the blower going full blast
Maybe someone can send me on the right path,maybe a link? Thanks,Huck50 :)

Offline Huck50

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Anyone have any experience with KitchenHoods.ca ??
« Reply #4 on: July 10, 2017, 08:10:17 PM »
I am in the market for a wall mount 30" range hood and i came across this company(Kitchenhoods.ca) located in British Columbia,so being a Canadian company,that got me interested.They seem to have a large variety of types and sizes and the prices are way cheaper than others I have looked at for the basically the same thing and they also have a decent warranty.
 The one range hood I am interested in is out of stock till early August,which is fine by me,but I don't normally buy without physically looking at an item I am interested in buying.
They seem to have good reviews,but I am not sure?!Anyone here have any bad experiences with this company? Thanks,Huck50