“Each appliance connected to a piping system shall have an accessible, approved manual shutoff valve with a nondisplaceable valve member, or a listed gas convenience outlet. Appliance shutoff valves and convenience outlets shall serve a single appliance only and shall be installed in accordance with 9.6.5.1.”- National Fuel Gas Code 9.6.5
In some cases we will find that a shutoff for an appliance will be downstream from another
shutoff meaning if one valve is turned off it will also turn off the gas to the other appliance. Gas valves must only operate one appliance at a time.