In a forced draft system, how does the pressure inside the furnace compare to atmospheric pressure?

In a forced draft system, the pressure inside the furnace is above atmospheric pressure. This is achieved by using a fan or blower to force air into the combustion chamber at a higher pressure than the surrounding atmospheric pressure.

This pressurized environment helps improve combustion efficiency by ensuring a consistent and adequate supply of air to the fuel being burned. The increase in pressure also helps prevent the ingress of unwanted air or gases from outside, which could negatively affect combustion efficiency and safety.

Thus, the correct answer indicates that the forced draft system intentionally maintains a higher pressure, facilitating controlled combustion processes crucial for optimal system performance.