On the calefactory, or calefactorium, one of the very few heated rooms in a medieval monastery. It wasn't only to keep monks warm in chilly winters though, it was also used to keep the important munimentum, or muniment chamber dry and warm to save important records and archives from damp and mold.
https://hell.twtr.plus/media/53d47b2210fb6649bdccf7bb35f1ebe3ac3619e73e0fbc6f31d4b93b225e64ed.file
https://hell.twtr.plus/media/08c6a5649b40b51c23e30e5dd34d126d9f61093aad0c6555fe38078c7895439a.file

The Conversation
How medieval monks tried to stay warm in the winter
Warm rooms were often very unusual in medieval times.

