What determines whether a boiler operates above or below atmospheric pressure?

The operation of a boiler above or below atmospheric pressure is primarily influenced by the method of air intake, which directly impacts combustion efficiency and pressure management within the boiler system. In a boiler, the air intake method determines how air is supplied to the combustion process. When a forced-draft fan is used to push air into the furnace, it can create positive pressure, allowing the boiler to operate above atmospheric pressure. Conversely, if the air intake relies on natural drafts, it may not achieve the same pressure levels, keeping the boiler operating at atmospheric or slightly negative pressure.

Understanding the combustion process and air-fuel ratios is crucial for efficient and safe boiler operation. Therefore, the method of air intake is a significant factor, as it dictates whether the combustion environment can sustain higher pressure levels necessary for certain applications. In contrast, other factors like the size of the furnace, the type of fuel used, and maintenance frequency do play roles in the overall performance and efficiency of the boiler, but they do not solely determine the pressure at which the boiler operates.