Directly heated DHW cylinders have their own gas burner and heat the water directly inside the cylinder. The hot gas transfers its energy to the water on its way from the burner via the cylinder to the flue outlet. If the water temperature drops, the burner starts automatically. The output and cylinder capacity can be individually matched to the actual DHW demand. Directly heated DHW cylinders therefore enable economical DHW heating, for example in detached houses or small commercial properties.