Grades 3–5 · Everyday Life
How does a tank keep hot water ready for a tap?
A hot-water tap can draw from water that was warmed earlier. In an electric storage water heater, an insulated tank holds that supply. An electric heating element transfers energy to the water around it. The insulation slows energy escaping to the cooler room.
In the diagramA tank stores water while an element warms itCutaway · water pressure moves water through the tankThermostatHeat called forCold inHot outInsulationElementElectrical energy warms the stored waterCold water in replaces hot water out.
A temperature control called a thermostat helps decide when heating is needed. When the water near its sensor is cool enough, the control calls for the element to heat. When that need is satisfied, it switches the element off. Heating can happen while every tap is closed.
Opening a hot-water tap gives water a route out. Pressure in the supply pushes cold water into the tank through a tube that reaches near the bottom. This incoming water replaces warmer water leaving from near the top. The heating element does not push water through the pipes.
The store is useful, but it is not unlimited. Drawing water replaces some warmed water with colder water, and reheating takes time. The picture separates the flow of water from the thermostat’s call for heat; real water temperatures and mixing change during use.
About this explanation
Starting knowledge: Know that electricity can warm an element and water can flow through pipes.
Sources
- A. O. Smith — Residential Electric Tank Water Heaters
- US Department of Energy — Residential Water Heaters Webinar