Red Seal Gasfitter — Class B Practice Exam

Which installation error can cause backdrafting in gas appliances?

1. Improper venting or seal failure

2. Insufficient gas supply pressure

3. Faulty gas appliance design

4. Lack of proper clearance

The correct answer is: Improper venting or seal failure

Backdrafting in gas appliances occurs when combustion gases, instead of being expelled outside, flow back into the living space. This can lead to dangerous situations, including the accumulation of carbon monoxide, which is harmful to health. Improper venting or seal failure is a critical factor that contributes to backdrafting. When venting systems are not installed correctly or have compromised seals, they can allow for the reverse flow of combustion gases. For instance, if the flue or vent is blocked, improperly sized, or poorly installed, it may not create sufficient draft to push gas emissions out of the building. Instead, these gases can be drawn back into the room, especially during negative pressure situations where indoor air is being exhausted faster than outside air can enter. In contrast, the other options, while they affect the operation and performance of gas appliances, are not direct causes of backdrafting. Insufficient gas supply pressure relates more to the appliance’s ability to properly function than to venting issues. Faulty appliance design may lead to inefficiencies or unsafe operation, but it does not inherently cause backdrafting if the venting is done correctly. Lastly, lack of proper clearance refers to the physical space around appliances for operational safety and airflow, not directly related