We present the design and capabilities of a high temperature gas flow environment for neutron diffraction and pair distribution function studies available at the Nanoscale Ordered Materials Diffractometer instrument at the Spallation Neutron Source. Design considerations for successful total scattering studies are discussed, and guidance for planning experiments, preparing samples, and correcting and reducing data is defined. The new capabilities are demonstrated with an in situ decomposition study of a battery electrode material under inert gas flow and an in operando carbonation/decarbonation experiment under reactive gas flow. This capability will aid in identifying and quantifying the atomistic configurations of chemically reactive species and their influence on underlying crystal structures. Furthermore, studies of reaction kinetics and growth pathways in a wide variety of functional materials can be performed across a range of length scales spanning the atomic to the nanoscale.