Undertank heater

Under Tank Heater (UTH), also called heating mat or heating pad, is a heating device created by the pet industry for husbandry of reptiles and amphibians. It is a flat piece of metal and plastic that provides a convenient and easy way to heat your reptiles, amphibian and even aquariums fish tanks. They provide constant heat, allowing you to create the optimal temperature gradient within the nursery

Use
The heater is usually placed at one end of the base, covering 1/3 of the base of the terrarium but alternately it may also be placed on a wall. The temperature emitted will pass through the terrarium walls and substrate, creating a temperature gradient throughout the enclosure. The hot zone is just above the heater; the opposite zone, the cold zone, is where the live food and the water bowl would be placed. A substrate between the pad and the tank is necessary, as is a thermostat or rheostat to prevent it from overheating and burning the animals. Malfunction in an under tank heater could result in higher temperatures which might harm animals or even start a fire.

Aquarium can also be heated by the use of heating mats which are placed beneath the aquarium. Glass is, however, a poor conductor of heat and thus reduces the efficiency of this method of heating.