What does a positive pressure before the furnace indicate?

A positive pressure before the furnace indicates a forced draft system. In a forced draft system, air is mechanically pushed into the combustion chamber by a fan or blower, creating a higher pressure inside the furnace compared to the surrounding environment. This setup helps ensure that combustion air is supplied efficiently, promoting better fuel combustion and system efficiency.

In contrast, a natural draft system relies on the buoyancy of hot gases to create a draft, which typically leads to a neutral or negative pressure condition rather than positive pressure. Gravity feed systems involve the use of gravity for fuel or fluid movement, which does not directly relate to the pressure dynamics present before a furnace. Negative pressure suggests an area where the air pressure is lower than atmospheric pressure, typically indicating a ventilation or airflow issue rather than a positive drafting method. Therefore, the indicator of positive pressure directly aligns with the operation of a forced draft system.