160 watts in a 20g tank is way overkill. You need to get a thermometer asap so you know the temps. You might very well be cooking your snake. I use 100 watt CHEs for my guys' temp 40g breeders and with the Herpstat going on them, I can easily keep em 82F+. Also if your room is really cold like you said, you can also buy sheet foam insulation from Home Depot and cut to fit and put it around the outside the cage to keep heat in.