All Webasto heaters are tested and approved to work in a temperature range from -30° to +40°C or more. The fuel used in very cold climates, where temperatures can fall considerably under 0°C (arctic diesel or winter diesel), is automatically mixed with additives to prevent freezing of the fuel. By using this fuel it ensures that no special preparation of the heater is needed. Basically, if your vehicle can drive, your heater will run as well.