warmer vs water boiler

warmer

noun
  • Something that warms, such as a heater or a soup. 

  • An introductory activity, for example in a lesson, to stimulate interest in a topic. 

  • A piece of clothing for warmth, such as a bodywarmer or leg warmer. 

water boiler

noun
  • An electric device which heats water up to boiling temperature. 

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