Wattage isn't what you really look for. You want the size of it to be about 1/3 the cage floor. That way the snake has room to get warm but also room to get cool. Most of important of all is you want a thermostat to run that UTH. You never want to let one run unregulated off wall power. They can get very hot and burn the snake or give the snake neurological problems from being overheated. Also you only want the substrate about 1/4-1/2" deep and you want to take the temp reading from the glass floor on the inside of the cage as snakes can and will push substrate aside to get to the bottom.