In what scenario is no duct opening allowed in an attached garage?

The correct answer is that no duct opening is allowed in an attached garage as a general safety requirement. This is primarily due to the potential hazards associated with allowing duct openings in such spaces. Garages can accumulate harmful gases, such as carbon monoxide from vehicles, as well as volatile organic compounds from stored chemicals and gasoline. If duct openings were permitted, these contaminants could be drawn into the living spaces of the home, posing significant risks to health and safety.

Regulations and building codes are designed to protect occupants by ensuring that air quality is maintained within the living areas. Therefore, prohibiting duct openings in attached garages is an essential safety measure to prevent pollutants from infiltrating the home environment. This practice aligns with safety standards aimed at maintaining clean and healthy indoor air quality for residents.

The other scenarios presented do not specifically address the inherent safety concerns associated with duct openings in garages, which relate directly to the potential for hazardous air quality issues.