oil burner vs water heater

oil burner

noun
  • A heating device which burns fuel oil; an oil furnace. 

  • A machine that uses oil as its fuel. 

  • A device whose operation causes apparent combustion of lubricating oil. 

water heater

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

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