SRY6-4 Sheathed Heater Darui Electric recommends: After adding a sheath, this electric heater has a larger heating area and faster heat transfer, effectively preventing carbonization of the heated medium. Since the heater is connected to the box via a flange and isolated from the heating medium, maintenance is convenient. During repair, simply remove the heating core and replace it with a new one. SRY6-4 Sheathed Heater After adding a sheath, this electric heater has a larger heating area and faster heat transfer, effectively preventing carbonization of the heated medium. Since the heater is connected to the box via a flange and isolated from the heating medium, maintenance is convenient. During repair, simply remove the heating core and replace it with a new one.