A natural gas (standing pilot) furnace usually requires what gas pressure at the manifold and burners?

A natural gas furnace with a standing pilot typically operates with a manifold pressure of about 3.5 inches of water column (W.C.). This pressure is standard for natural gas appliances to ensure they ignite properly and operate efficiently. The 3.5 in. W.C. pressure allows the pilot light to remain lit and the burners to ignite correctly when the furnace calls for heat.

Higher pressures, such as those indicated in the other choices, could lead to an overly rich mixture of gas, which can cause issues such as delayed ignition, increased carbon monoxide production, or even damage to the furnace components. Likewise, if the pressure were too low, the burners may not operate effectively, leading to incomplete combustion and reduced heat output. Therefore, the 3.5 in. W.C. specification ensures a safe and efficient operation of the furnace, aligning with manufacturer guidelines and industry standards.