Which type of draft involves a fan at the stack that pulls air through the furnace?

The type of draft that involves a fan at the stack which pulls air through the furnace is referred to as induced draft. This system operates by creating a negative pressure within the combustion chamber, ensuring that flue gases are efficiently removed from the furnace. The fan located at the stack assists in drawing the combustion air into the furnace while expelling exhaust gases, which is crucial for maintaining optimal furnace performance and efficiency.

Induced draft systems are advantageous because they help to prevent the escape of combustion gases into the workplace and can improve the overall efficiency and control of the combustion process. They are particularly useful in applications where maintaining the right atmospheric conditions is important for safety and operational efficiency.

In contrast, forced draft systems use a fan to blow air into the furnace, increasing the pressure within the combustion chamber. A balanced draft system combines both forced and induced draft principles to optimize the airflow into and out of the furnace. Negative pressure draft is a less common term and typically describes conditions that can lead to problems such as backdrafting, which is not aligned with the function of a fan in this context.