Last week I wrote about the cloister, which was the place where the monks spent most of their time when they weren’t in church. The cloister was, at least in the early Middle Ages, mostly unheated and the light on wet or snowy winter days would have been too poor for reading or copying books, which is what the monks were doing there. There would also be days when it was simply too cold to sit in the cloister, even if there were braziers at strategic points.
On those days the monks could sit in the calefactorium (warming house or warming room). In most monasteries it was just a large room, but in Cistercian monasteries it was a separate building.
It was called a warming room because it had a fireplace, sometimes two. It was one of only three rooms in a monastery that had a fire, the other two being the kitchen and the infirmary.
The fire was lit on All Saints Day (1st November) and was allowed to burn until Good Friday (anywhere between 20th March and 23rd April).
One of my sources suggests that clothes were dried in the warming room in winter, which would explain the two fireplaces. I think the size of the room and the number of monks it might have to accommodate explain them fairly adequately.