In the Northern Hemisphere, it’s about time for the weather to become cooler. That’s why I thought about this vocabulary pitfall today…
In standard American English, the word “air conditioner” only means “a machine that makes the air cooler and drier.” It’s very surprising to us to see someone say “I turned on the air conditioner because I was cold.” However, in Japanese and some other Asian languages, the phrase means “a machine that changes the air’s temperature and humidity.”
In American English, we would probably say “I turned on the heater because I was cold.” Most houses have central heating (warm air is pushed to all parts of a house or apartment). It may use electricity or gas. That’s still just called “the heater,” though. Some people have wall heaters, portable electric heaters, or other kinds of heaters. “Heater” is a general word that can be used for many different things.
Small heaters that you can carry are called portable heaters, etc., not “stoves.” The word “stove” almost always means the thing in the kitchen that you cook on. Only very old houses use a special kind of wood stove for heating. These stoves are big, heavy, and made of metal. (A few modern houses have a heat stove as an old-fashioned extra thing.) Of course, a long time ago, the cooking stove and the heating stove were the same thing!
You may have a (Japanese, etc.) “air conditioner” on your wall or ceiling that both heats and cools. In this case, I recommend saying “the heater” when you’re talking about using its heating function. If you say “air conditioner” when you’re talking about heating, it will cause most English-speaking listeners to be confused.
My heater and air conditioner are controlled by the same controller on my wall, called a thermostat. But I still say “Honey, can you turn on the heater?” or “Oh, why is the air conditioner on? Turn it off and open the windows!”
Anyway, basically: “air conditioner” means cooling (only) and “heater” means “heating.” It’s true for apartments, houses, businesses, schools, and cars!