central heating vs fan heater

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. 

fan heater

noun
  • an electric heater fitted with a fan which blows out hot air. 

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