What's the minimum temperature that it's safe to keep chins in?

I'm familiar with the max temperatures that chins should be kept in, but what about the coldest?



I ask because I'm realizing that the new rental I've just moved into has very poor insulation. It's freezing in here and it's not even winter yet. What would ya'll say is the minimum safe temperature for chins to be living in?



My little dudes have fleece liners as well as a fleece covered tube and fleece hidey house, so that should help keep them a little warmer. But I need to know if I should move them to my boyfriends (much warmer) house when the temperature drops.



Thanks!