Obtain the specifications included with the operational instructions for the gas appliance. The specifications should include the British Thermal Unit (BTU) or the Standard Cubic Foot (SCF) for gas consumption.
Size the gas regulator according to the gas inlet pressure. Your local gas utility will have the inlet pressure listed on the main gas meter for your home or you can call them for the information.
Read the outlet pressure required for the appliance on the specification sheet from Step 1. The gas regulator must be sized for the proper outlet pressure to operate the appliance.
Size the regulator according to both the inlet and outlet gas pipe diameter. In most cases, the inlet and outlet pipe diameters may have to be the same.
Designate which type of gas you are connecting to, natural gas or propane.