Corrosion is formed in the flue pipe when:

The formation of corrosion in the flue pipe is primarily influenced by the temperature of the flue gases in relation to the dew point. When the flue gas temperature is below the dew point, condensation occurs within the flue pipe. This condensation can consist of water vapor that combines with acidic components found in the flue gases, such as sulfur dioxide and carbon dioxide. The resulting mixture leads to acidic conditions that promote corrosion of the metal surfaces within the flue pipe.

Maintaining temperatures above the dew point is crucial in preventing this type of condensation from occurring. Therefore, when the flue gas temperature is below the dew point, the environment becomes conducive to corrosion, highlighting the importance of temperature management in preventing damage to the heating system.