It's not something that heats the hot water. It heats regular tap water to shower, wash your hands, cook, and clean. It takes the cold water from a water supply and heats it. It then pumps it throughout your home when you open a tap or start your clothes washer. They are used to warm potable water. It's in many ways like the term air conditioner, which you most likely heard about. Just like an air conditioner, which is a machine for cooling air. The term conditioner means filtering and dehumidifying. If you're looking to buy one, you should consult https://www.marvellous.sg/aircon-not-cold/. They specify in selling water heaters and aircon.