I don’t know which building codes have been adopted in your area and I’m not sure what “ERC guidelines” means… maybe IRC (International Residential Code)?
Smoke / fire penetration and possibility of Carbon Monoxide leakage
into the living quarters are the biggest concern…
SECTION M1503 RANGE HOODS
Range hoods shall discharge to the outdoors through a single-wall 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.
Attached garage is considered the same building.
As far as garage - house wall penetrations
and safety issues, the following are from the 2006 IRC (not included in 2009 and 2012 releases, unless they associated it with different paragraphs).
SECTION R309 GARAGES AND CARPORTS
R309.1 Opening protection.
Openings from a private garage directly into a room used for sleeping purposes shall not be permitted. Other openings between the garage and residence shall be equipped with solid wood doors not less than 13/8 inches (35 mm) in thickness, solid or honeycomb core steel doors not less than 13/8 inches (35 mm) thick, or 20-minute fire-rated doors.
R309.1.1 Duct penetration.
Ducts in the garage and ducts penetrating the walls or ceilings separating the dwelling from the garage shall be constructed of a minimum No. 26 gage (0.48 mm) sheet steel or other approved material and shall have no openings into the garage.
R309.1.2 Other penetrations.
Penetrations through the separation required in Section R309.2 shall be protected by filling the opening around the penetrating item with approved material to resist the free passage of flame and products of combustion.
Maybe you should call your local building department and ask about it. It would be the best way to convince the home inspector if you could quote… or even get in writing what’s required in your local jurisdiction.
If, based on their answer, this is a violation in your area, ask if a range hood is required or if it can be a re-circulating type. You unit may be already equipped with such feature (all it takes is to reposition the blower inside of some models) and even if you need to get a new one to satisfy the inspector the basic hoods aren’t that expensive. Some insulation to fill the air duct hole and piece of drywall to cover the opening inside the garage would take care of this firewall breach.
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