Gas pressure in lines that supply poultry houses is reduced at two or three different places, depending on the type of fuel supplied to the house. For houses that use second-stage regulator is usually outside of the house and close to the middle of the brood area, and the third-stage regulator is in the gas control valve on the brooder. Houses that use natural gas will usually have only the second- and third-stage regulators. Regulators on brooders control brooder manifold pressure, or the pressure of the gas just before it is burned.
Source : msstate.edu