Which best describes balanced draft?

Balanced draft refers to a system where both forced draft and induced draft fans are used to maintain optimal air pressure within a furnace. This arrangement allows for precise control of airflow and pressure, enabling the furnace to operate efficiently. By utilizing both types of fans, the system can keep the furnace pressure below atmospheric levels, which prevents the escape of flue gases and ensures proper combustion conditions. The use of induced draft fans helps remove the combustion gases from the furnace while forced draft fans effectively supply fresh air into the system, leading to a balanced and efficient operation.

In contrast, the other descriptions do not accurately capture the functionality of balanced draft systems. Induced draft alone cannot maintain atmospheric pressure; rather, it works to pull gases out of the furnace. Natural draft relies on temperature differences for air movement, which may not always ensure an optimal supply of air under varying conditions. Meanwhile, relying solely on forced draft fans may not meet all pressure requirements effectively, especially in systems that require careful management of airflow.