4th Steam Practice Test 2026 – The All-in-One Guide to Master Your Exam!

An induced draft fan creates a negative pressure inside the boiler furnace by pulling combustion products out through the stack. This suction draws air through the burners and up and out of the furnace, keeping the furnace zone at a lower pressure than the surrounding area. That negative pressure helps contain flue gases and ensures they flow in the right direction toward the stack. In contrast, a force draft fan pushes air into the furnace, generating positive pressure and aiding combustion. A balanced draft system uses both fans to keep the furnace near atmospheric pressure, while a blower is a general term for a fan and isn’t specifically tied to creating negative furnace pressure.