heating vs water heater

heating

noun
  • A system that raises the temperature of a room or building. Compare heater. 

  • The act of making something hot. 

adj
  • Causing heat. 

water heater

noun
  • An appliance for heating water above its ambient temperature, generally for domestic use. 

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