I also started with a good inch and a half of aspen at first but now i have reduced it to about half an inch. The heat gets through the aspen no problem connected to the thermostat. One of my snakes sits happy on the aspen, the other pushes it to the side all of the time. His temps are spot on to. Its no problem as he pees and poops always where there is aspen. So i would go with a reduced amount of aspen.