central heating vs furnace

central heating

noun
  • Any of various heating systems in which a central source of heat is used to distribute heat (and sometimes hot water) throughout a building in a controlled manner. 

furnace

noun
  • A device that provides heat for a building; a space heater. 

  • A place or time of punishment, affliction, or great trial; severe experience or discipline. 

  • Any area that is excessively hot. 

  • An industrial heating device, e.g. for smelting metal or baking ceramics. 

verb
  • To heat in a furnace. 

  • To exhale like a furnace. 

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