Basics

• An under tank heater is a thin mat with an adhesive backing that sticks to the underside of a glass enclosure. Inside this mat is a long wire running in a zigzag pattern. When the under tank heater is plugged in to a power outlet, an electric current runs through the wire, heating up the pad and raising the ambient air temperature of the enclosure.
  
  

Sizes

• ZooMed, the official manufacturer of under tank heaters, produces four sizes to accommodate different sized tanks. There is a 4-inch by 5-inch size, which is appropriate for 1 to 5 gallon tanks; a 6-inch by 8-inch size appropriate for 10 to 20 gallon tanks; an 8-inch by 12-inch size for 30 to 40 gallon tanks; and an 8-inch by 18-inch size appropriate for 50 to 60 gallon tanks. In most instances, matching the appropriate sized heater with the right tank will result in an increase of 2 to 8 degrees Fahrenheit in the tank.
  
  

Uses

• Under tank heaters are designed to act as a secondary heat source, meaning that they will raise the ambient air temperature of the enclosure but not provide a warming area for your reptile. Warming areas, or basking areas, should be created with heat lamps and heat bulbs that concentrate high temperatures, usually around 90 to 100 degrees Fahrenheit depending on the reptile, in a single area. Under tank heaters can be left on 24 hours a day to keep the tank warm during the cool nighttime hours.
  
  

Warnings

• The under tank heater should not be removed once it is adhered to the glass, as this could potentially damage the internal components. An under tank heater should also not be placed right below water, like in a vivarium or terrarium, as this will cause stress cracks in the glass, leading to leaks. If the entire bottom of your tank is filled with water, then you can place the under tank heater on the side of the tank, but it should be placed above the waterline and in an area where your reptile cannot directly touch the same surface it is touching, as it could lead to burns.