Insertion heaters cannot be fitted to certain vehicles, e.g. some construction machinery, tractors, trucks, smaller gensets, and in exceptional cases passenger cars. The Calix Professional Heater (PH) was developed for these vehicles and gensets. The PH works based on a self-circulating principle and is connected to the cooling system outside the engine block using a hose connection (20 mm). The heater is equipped with overheating protection, a thermostat, and a rubber sealing for increased service life and reliability. The Calix PH is available in two versions: one designed for the high temperature area, for example for frequently used machinery, and one for the low temperature area, for example for stationary engines that must be warm and ready to start for long periods.