If your pond occupies living creatures, a pond heater will be needed to keep the pond water at a stable temperature to ensure proper health for pond fish. Pond heaters are situated at the bottom of the pond. Pond heaters have a rubber bumper around them to prevent them from touching the sides or bottom of the pond. The controller for the pond heater should always be protected from getting wet. To determine the size of pond heater your pond requires, consider that it will take a 1000 watt heater to heat 250 gallons of water to 10 degrees Fahrenheit. Prices for pond heaters are determined according to the heater's capacity. Pond heaters range from approximately $440 to $800 online.