DHX Plus models feature both the robust and trouble-free Direct Coil heating system and Advanced Flow Control. Stiebel Eltron's most advanced water heating technology, the Direct Coil heating system is self-cleaning for superior limescale resistance. Advanced Flow Control, patented in Germany, is exclusive to Stiebel Eltron tankless heaters. If hot water demand exceeds working capacity, Advanced Flow Control automatically maintains consistent temperatures by slightly reducing flow. DHX plus models heat water endlessly on demand at 99% efficiency. No venting is required and the compact European design can be installed with the unit visible. The DHX series excels at supplying water at a constant temperature, but the amount of hot water and its temperature depends on the incoming cold-water temperature and the size of the DHX model. The correct model size must be chosen by using the DHX Sizing Guide.