ReptiTherm® U.T.H. Under Tank Heaters are an ideal 24 hour primary or secondary heat source for tropical or temperate reptilian species. All of Zoo Meds Under Tank Heaters are UL/cUL approved (GS/TuV/CE in Europe) and contain a solid state nichrome heating element. These under tank heaters permanently adhere to your terrarium, forming a solid bond for optimum heat transfer. Available in 4 sizes. mini, small, medium and large.