What does the term "draft" refer to in a gas furnace?

The term "draft" in the context of a gas furnace specifically refers to the airflow that moves combustion gases out of the flue. Draft is crucial for the safe operation of a gas furnace, as it ensures that exhaust gases are effectively vented outside the home, preventing harmful gases from re-entering the living space. Proper draft is essential for efficient combustion and to maintain the required pressure differentials within the furnace.

In addition to its role in venting gases, draft can also influence the overall efficiency and safety of the heating system. A negative draft, or a draft that is not strong enough, can lead to incomplete combustion, while a positive draft may indicate an issue with the flue or chimney system that could affect performance.

Understanding the concept of draft helps technicians diagnose issues with the furnace's venting system, such as blockages or leaks that could disrupt the safe and efficient operation of the unit.