What is the most common cause of flue gas spillage from gas appliances?

The most common cause of flue gas spillage from gas appliances is negative air pressure caused by mechanical systems. This phenomenon occurs when exhaust fans, kitchen hoods, or HVAC systems create a pressure differential within a building. If the air pressure inside the home is lower than the pressure outside, it may cause the appliances to draw air from the flue instead of from the room, leading to spillage.

In gas appliances designed to expel combustion gases properly, maintaining a balanced air pressure is crucial for efficient and safe operation. When negative pressure is present, it can disrupt this balance, preventing the flue gases from venting outside effectively, thus increasing the risk of backdrafting harmful gases into the living space.

This situation emphasizes the importance of proper ventilation and ensuring that mechanical systems are correctly balanced to prevent flue gas spillage, which is vital for both safety and appliance performance.