athanor vs calefactor

athanor

noun
  • A furnace or stove designed and used to maintain uniform heat, primarily used by alchemists. 

calefactor

noun
  • A heater; one who, or that which, makes hot, such as a stove, etc. 

How often have the words athanor and calefactor occurred in a corpus of books? (source: Google Ngram Viewer )