Stationary and mobile steam generators are widely used in low ambient temperatures, for example in areas described by the Köppen world map as subarctic. Such equipment is often used in oil and gas fields. At the moment, the existing standard boiler plants are outdated. The purpose of this work is an experimental study of a coiled-type direct-flow steam generator developed by the authors in the winter period at low ambient temperatures. The tasks to be solved to achieve the goal are associated with obtaining experimental data at different operating modes of the installation, their processing and the development of empirical coefficients of gas movement inside the coaxial cylinders of the steam generator. In addition, another task is to develop a theoretical basis for the obtained experimental data. Based on the results of the work, the dependences of pressure and temperature on fuel consumption in various modes were obtained. Statistical analysis was applied to the data obtained. The authors have developed equations for calculating the convective part in the process of radiant-convective heat transfer in coaxial gas ducts, taking into account the design features of a once-through coil-type steam generator. Finally, promising directions for further improving the efficiency of steam generators of this type are proposed.