There are mainly four situations in which the word ‘gas bypassing’ is used in boilers:
1. Despite adequate provisioning of HS, anticipated amount of flue gas cooling does not take place in the boiler, leading to reduced thermal η and loss of heat. Essentially, gases here are bypassing the HS. This happens when part of the flue gases go around the tube banks because of excessive end gaps or dislocation of gas deflection baffles. This is called gas bypassing the tube banks.