I use Honey's water bowl as my temperature gauge. Her water bowl is inside the hutch so if it freezes then it has gone below freezing in her hutch. It has only happened once before today, where it has happened again. She has snugglesafes to cosy up to, and she had two together last night, which still had a bit of heat in them this morning. As we are having similar temperatures for the rest of the week I'm thinking of bringing her into the conservatory.