A. The Autoterm DE015 Air Pipe is designed to distribute heated air efficiently from compatible Autoterm Air 4D diesel heaters to the living or working space. Its 90 mm diameter provides the airflow required by the Autoterm Air 4D heating system, helping maintain proper heater performance while delivering warm air throughout trucks, campers, RVs, boats, commercial vehicles, and other enclosed spaces. Using the correct duct size supports safe operation, improves heating efficiency, and helps maintain long-term reliability.