What is a potential consequence of vent blockage in a gas furnace?

Vent blockage in a gas furnace can lead to significant safety hazards. When the venting system, which directs combustion gases outside, becomes obstructed, harmful gases such as carbon monoxide can accumulate within the home. This buildup poses a serious health risk to occupants because carbon monoxide is odorless and colorless, making it difficult to detect without proper alarms. Additionally, a blocked vent can prevent the furnace from operating correctly, potentially causing overheating and triggering system failures that could lead to dangerous situations, including fire.

The other options do not align with the implications of vent blockage. Increased efficiency would be unlikely as vent blockage restricts airflow and can force the system to work harder, leading to reduced efficiency. Higher fuel costs may occur as a secondary consequence due to the furnace needing more fuel to operate ineffectively, but this is not the direct or immediate risk associated with blockage. Lower emissions would also not be a result of vent blockage; in fact, emissions could rise due to incomplete combustion caused by improper venting. Thus, safety hazards are the most significant and immediate consequence of vent blockage in a gas furnace.