Patent ID: 7085482

Claim:
An aquarium water heater comprising: a hollow heat-conducting internal tube; an electric resistance heater element with electrical connections, the heater element disposed adjacent an outer surface of the hollow heat-conducting internal tube; a temperature thermal cut-out switch electrically connected to the heater element for overheat protection when the temperature of the heater element exceeds a predetermined maximum value; a hollow heat-conducting external tube spaced from and circumscribing the internal tube and the heater element; a heat-conducting, electrically-insulating polymeric filler filling a space between the internal tube and the external tube and sealing the heater element between the internal tube and the external tube; a controller electrically coupled to the heater element to activate and deactivate the heater element; an indicator electrically coupled to and responsive to the controller; and a water temperature sensor electrically coupled to the controller, the water temperature sensor sensing the temperature of water into which the heater is at least partially immersible and providing a corresponding electrical signal to the controller and monitoring the temperature of the water regardless of whether the heater element is activated, the controller activating the heater element when the temperature of the water is below a first predetermined minimum temperature and deactivating the heater element when the temperature of the water is above a first predetermined maximum temperature, and further activating the indicator when the water temperature is below a second predetermined minimum temperature and when the water temperature is above a second predetermined maximum temperature.