Is it called a hot water heater or water heater?
It's because "hot-water" is a compound adjective, modifying "heater". It's not for heating water, it's for heating a house with hot water. There are many types of heaters that heat water, but only a hot-water heater is used for providing heated water for domestic use. A hydronic boiler also heats water, but it's only for use in radiators.The name "Hot Water Heater" is completely wrong for any use. There is no need to heat hot water. IT has always been "water heater". The term hot water heater has just been used for years because people don't realize the difference. It has always been WATER HEATER.The first answer is jibberish and makes no practical sense at all.