Rabbits are outside animals, who use their fur to keep themselves warm. The proper temperature range for a rabbit is between 50°F and 90°F (between 10°C and 32°C). Because rabbits do not have much body fat, anything below this temperature can be dangerous or even fatal.
If the temperature falls below 45°F, water bottles should be covered or frozen so that they won’t become dangerously hot when filled with water.
Rabbits living inside should have a temperature between 65°F and 75°F (18°C and 24°C), with a relative humidity of 45 to 55 percent. If the temperature falls below 60°F, provide supplemental heating. Remember that rabbits like to hop and should have plenty of space to run around to keep warm.

FAQS
how can I keep my rabbit warm on the cold winter days?
It is important to protect rabbits from extremely cold temperatures. Bring your pet inside if it’s too cold for you, it is too cold for them! During particularly chilly days, make sure their cage or hutch has access to dry bedding that cannot become damp when they are allowed out to use the bathroom. And of course, ensure that you are using a water bottle that is not too hot for them!
If it’s below 50°F outside, rabbits should be brought indoors. and If your rabbit lives outdoors, he or she will need shelter with dry bedding to protect them from drafts and dampness. If the temperature falls below 45°F, water bottles should be frozen or covered.
65°F-75°F is the ideal temperature for indoor rabbits, with a humidity of 45 to 55 percent. If the temperature falls below 60°F, provide supplemental heating. Make sure your rabbit has enough space to hop around and stay warm!