Penn Plax Aquarium Heater Fully Submersible Within 1 Degree of Accuracy 75 Watt Heats Up to 15 Gallon Tank Aquarium heater sets and maintains the temperature in your tank within 1 degree accuracy. Features both Fahrenheit and Celsius temperature with easy to read gage. Heater is fully submersible and can be placed horizontally or vertically in your tank. Has a preset temperature to 76 degrees Fahrenheit but is also easily programmed. Heater is safe to use on larger fish tanks and aquariums up to 20 gallons in size.