Which is the best description of natural draft furnace operation?

Natural draft furnace operation relies on the principles of gravity and buoyancy to move combustion gases out of the furnace and through the exhaust system. When the air inside the flue pipe is heated by the combustion process, it becomes less dense and rises due to the buoyancy effect. This upward movement creates a natural draft that allows fresh air to enter the combustion chamber as the heated gases make their way out. This process is efficient in typical operating conditions, particularly when the furnace is properly vented and installed.

In contrast, options that focus on mechanical fans or sealed systems do not apply to natural draft systems. Mechanical fans actively push or pull air and combustion gases, while sealed combustion systems utilize different venting strategies that prevent natural drafts from occurring. The natural draft system is also distinct in that it does not require any special ventilation systems aside from standard flue pipes to enhance the chimney effect created by temperature differences.