ReptiTherm® Under Tank Heaters are an ideal 24-hour primary or secondary heat source for tropical or temperate reptilian species. All of Zoo Med’s 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. Inexpensive, low wattage heaters. Excellent secondary heat source. Available in the following sizes: Mini: 1 - 5 gallon (4" x 5"), 4 w Small: 10 - 20 gallon (6" x 8"), 8 w Medium: 30 - 40 gallon (8" x 12"),16 w Large: 50 - 60 gallon (8" x 18"), 24 w