HallWasser 20.5 mm flow meter with a stainless steel sensor, designed as a warm water heater flow sensor YFB1S. Specifically sized and built for warm water heater circuits, this Durchfluss (flow) sensor model YFB1S provides accurate flow readings in hot water preparation systems. The Edelstahl (stainless steel) sensor delivers durable, reliable performance in challenging hot water environments, helping you monitor and control heating systems with confidence. Compact 20.5 mm diameter supports easy installation and retrofit in existing piping and fittings, while offering consistent, dependable measurements in everyday use. Key benefits - Accurate flow measurement for warm water preparation - Durable stainless steel sensor for long-term reliability - Compact size enables easy installation and retrofit - Model YFB1S is tailored for warm water heater installations - Clear compatibility with hot water circuits and heating systems Use scenarios - Residential hot water heater installations to verify flow and support proper heater operation - Commercial or multi-unit buildings with hot water distribution to monitor circulation and ensure adequate supply - Retrofit projects in solar thermal or heat pump based hot water systems to track flow and maintain performance