calefactory
noun
cal·e·fac·to·ry ˌka-lə-ˈfak-t(ə-)rē 
plural calefactories
: a monastery room warmed and used as a sitting room
Word History
Etymology
Medieval Latin calefactorium, from Latin calefacere to warm — more at chafe
First Known Use
circa 1681, in the meaning defined above