What is the passageway within a chimney or vent called where combustion gases pass?

The passageway within a chimney or vent where combustion gases are routed is called a flue. This term specifically refers to the channel that carries smoke and gases away from a fireplace, furnace, water heater, or boiler and out of the building. The flue is designed to facilitate the efficient and safe removal of these gases, ensuring proper ventilation and minimizing any potential hazards such as the buildup of toxic fumes or moisture.

Understanding the term "flue" is essential for anyone involved in the installation, maintenance, or inspection of heating systems since it plays a critical role in the system's performance and safety. The proper sizing and integrity of the flue are vital to ensure that combustion gases are effectively expelled, preventing backdrafts or venting problems that could lead to hazardous situations.