This heated "safety stone" is designed as a secondary heat source. The insulated nichrome wire element runs continuously back and forth throughout the heater, creating an even heat source with no "hot spots." The element is water-resistant to prevent possible electric shock if heater gets wet. Washable surface prevents bacteria build-up. Features full coverage, completely encapsulated heating element. The Standard Rock Heater SIZE - (10"W x 7"D x 2"H) The heater takes approximately 2 to 3 hours to heat up and should feel warm to the touch. The rock surface heats to temperatures of between 90 to 110 F.