I had the same problem last winter and I tried to fix it with strategically timed usage of the heater by putting it on a timer switch. It didn't work well though as it caused friction with my landlady/best friend. This year what I've done so far since the temperature has dropped (insert joke about canada and cold temperatures) is a heat lamp, only what I did is I bumped it up from a 60 watt to a 100 watt and so far, even when the external temp of my room was high 60's, the ambient temperature in Nagini's enclosure has stayed in the low 80, with a hotspot of 89.