The Caleffi XP polyphosphate dosing unit, code 545950, is an effective solution for preventing limescale formation in domestic hot water systems. Installed on the cold water supply pipe to the boiler, it proportionally releases polyphosphates that protect internal surfaces from scaling and corrosion. Equipped with 1/2" M x 1/2" F connections and supplied with a refill of crystals, it ensures an average treatment duration of 35-40 m³ of water, helping to maintain the efficiency of the system over time.