What size orifice is needed for a natural gas appliance operating at 30000 Btu with a pressure of 3.5 in/wc?

The correct sizing of an orifice for a natural gas appliance is crucial for ensuring the appliance operates correctly and efficiently. When determining the appropriate size of an orifice for an appliance with a specific input BTU rating and gas pressure, it's essential to refer to standard charts that correlate orifice sizes to gas flow rates at given pressures.

In this case, the appliance operates at a BTU input of 30,000 with a pressure of 3.5 inches of water column (in/wc). Standard gas appliance tables indicate which orifice size will allow the appropriate volume of gas to flow, ensuring that the appliance operates safely and effectively without issues such as incomplete combustion or excessive emissions.

For an appliance rated at 30,000 BTU at 3.5 in/wc, orifice size #38 is determined to be the appropriate choice based on conversion calculations and flow rate requirements for natural gas.

This choice aligns with the need for sufficient gas flow while maintaining a balance with the applied gas pressure. Other sizes, such as #35, #40, or #42, would either restrict gas flow too much or allow too much gas, leading to inefficiencies or safety concerns. Thus, the correct orifice size, #38, ensures