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I had a contractor install a hood vent. He ran a foil pipe up towards the roof and tie it @ 6 in below the turbine vent (whirley birds). Is this adequate for all the fumes to escape out? Is this ok? He told me to run it out through the roof it would cost more money.

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    When you say "foil pipe" do you mean flexible metal duct, like with corrugations and can be expanded by pulling out? Nov 10, 2016 at 16:26
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    It always costs more in the short term to do it right, but in the long term, you could have costly problems. My house's clothes dryer vent goes partway into the attic, no where near a vent, so I get free flammable lint insulation nearby. Nov 10, 2016 at 19:00

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TL;DR:

  • It is explicitly not to code to exhaust into the attic or to use foil pipe
  • It's a bad idea anyway because it puts smoke, grease and warm humid air into your attic which can cause mold growth

2015 International Residential Code, Chapter 15:

M1501.1 Outdoor discharge.

The air removed by every mechanical exhaust system shall be discharged to the outdoors in accordance with Section M1506.3. Air shall not be exhausted into an attic, soffit, ridge vent or crawl space.

Foil pipe is also not allowed:

M1503.2 Duct material.
Ducts serving range hoods shall be constructed of galvanized steel, stainless steel or copper.

I'd also say aside from the material, foil pipes don't meed the requirement of having a "smooth interior surface":

SECTION M1503 RANGE HOODS

M1503.1 General.

Range hoods shall discharge to the outdoors through a duct. The duct serving the hood shall have a smooth interior surface, shall be air tight, shall be equipped with a back-draft damper and shall be independent of all other exhaust systems. Ducts serving range hoods shall not terminate in an attic or crawl space or areas inside the building.

Also note that range hoods are very explicitly not allowed to exhaust into an attic, though there is an exception for hoods that are specifically built to exhaust elsewhere:

M1503.1 Exception: Where installed in accordance with the manufacturer’s instructions, and where mechanical or natural ventilation is otherwise provided, listed and labeled ductless range hoods shall not be required to discharge to the outdoors.


This of course can vary by jurisdiction (eg: your jurisdiction may follow a different version of IRC, have their own amendments, or not follow it at all), and the final call is up to the AHJ (Authority Having Jurisdiction, aka inspector). You can likely call your local building permits department to be sure.

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I don't know where you live, but something to consider is that you're dumping warm, moist air into a potentially cold zone. So some of that air can/will condense in there in winter. Since attics tend to be filled with untreated wood, that means you're creating all the necessary conditions for mold to grow. That can potentially negatively affect your home air quality.

Code or not, I'd get it vented out of the roof.

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    Besides which, a kitchen hood is venting smoke and grease, neither of which is something you want collecting in the attic or in the roof vent. Nov 11, 2016 at 15:54

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