H2O heater

The plumber came to fix the water heater and to replace a flush system for the toilet. The water heater system here is quite interesting. In America, I am used to a big water heater that goes in a closet somewhere and heats up water and keeps it heated in a reserve tank. Here, the device works differently. The pilot light remains on, unless turned off. When a hot water faucet is turned on, then the pilot sparks a big burner on and the water passes through small metal tubing where it will heat up. The temperature can be relatively warm or super hot, but that is knob-adjustable on the device. According to others who have used them, they are very efficient and last for years. They supposedly last longer than the reserve tank heaters I am used to seeing in America. Hmmm, I wonder if this is available in the US???