These Hydor® Theo heaters are the safest submersible heaters we could find in the market today. They are completely submersible, ULapproved, salt water compatible and shatterproof. Instead of the typical metal element in a breakable glass tube, these heaters utilize a polymer sheet that uniformly heats a shatterproof glass tube. The temperature is controlled and maintained by a highly precise micro-switch controller, adjustable from 70 to 89ºF. Heaters are 115V/ 60 Hz with a 6’ cord. One-year warranty.