Under-tank heater

An under-tank heater, often called a heat mat, is a thin adhesive heating pad placed under or on the side of an enclosure to warm the substrate or an adjacent hide rather than heating the air directly. It is a common choice for species that thermoregulate partly through belly heat, or as a supplemental warm spot alongside an overhead basking bulb.

Under-tank heaters should cover only part of the enclosure floor, generally under one end, so the animal can still move off the heated area entirely, and they need a thermostat with the probe placed on the substrate directly above the mat, not just taped to the mat itself, since substrate depth changes how much heat reaches the surface. Glass tanks conduct heat differently than PVC or wood enclosures, which affects how warm a mat needs to run to hit the same surface temperature.

The most serious and well documented risk with under-tank heaters is thermal burns, which happen when a mat runs unregulated or when substrate is too thin over the heated area, letting the surface get far hotter than intended. Running any heat mat without a thermostat, or covering the entire enclosure floor with one, are the two mistakes most often linked to burn injuries in reptile keeping.