Properly operating natural draft systems create what type of air pressure?

Properly operating natural draft systems are designed to create negative air pressure within the combustion chamber. This negative pressure is essential for facilitating the flow of combustion gases upward through the flue and ensuring that fresh air is drawn into the system for combustion.

The principle behind natural draft systems relies on the difference in density between cooler ambient air and the warmer gases produced during combustion. As gases rise through the flue due to their lower density, they create a vacuum or negative pressure that pulls air in from the surroundings, which is necessary for efficient fuel combustion.

In contrast, systems that operate under positive pressure could lead to dangerous conditions, such as backdraft or the escape of combustion gases into the living space. Neutral pressure indicates a balance where the system is neither drawing air in nor pushing it out, which is not ideal for the operation of combustion systems. Variable pressure would imply fluctuations in air pressure that could compromise safety and efficiency. Therefore, the correct identification of negative pressure is crucial for properly functioning natural draft systems.