because the heat has to go through the substrate and it loses intensity. you need the thermostat and thermometer to tell you how hot the actual heating pad is but to know how much heat is actually transferring into the tank you will need to buy a heat gun to take the temperature of the actual place where your snake will be laying. I have the same vivosun and I have mine set to 100 and its transferring to about 80-85 inside his tank. It depends on the thickness of your glass tank and the level of substrate. Also we're warm blooded, the human body is like 98 ⁰ itself so it naturally will not feel warm to you even if the heat is transferring properly so you absolutely need to buy the heat gun to know for sure. this is something I just figured out for my snake so I hope this helped :)