How Can You Heat With Water?

Everybody knows that water starts to boil at 100°C. Thereby, water vapour is generated. If you submerge a thermometer in the water, you will notice that the temperature doesn’t change any more. Even if you turn up the heat on the oven, the temperature of the boiling water will remain constantly at 100°C until all the water has evaporated.

So, a lot of energy is needed for the transformation of water into water vapour. When you place a glass lid over the pot, the water vapour will condense on the cold lid. During the condensation of the water vapour, energy is released as heat. This heat is called the condensation heat of water. This method of energy recovery is exploited to warm cold water, for example.

How does the warm water get into the water pipe?

Hot water for brushing our teeth in the morning - we expect it! But where does it come from, actually? Usually the cold water is heated in a central-heating boiler (condensing boiler). Hydrocarbons are used as the energy carriers in such boilers. They generate heat when they are burned to ashes. This heat is used to warm up cold water. The combustion products are carbon dioxide and water vapour. A concrete example: Natural gas consists of methane. That is one carbon atom and 4 hydrogen atoms. When combusted with air - 2 oxygen molecules - one carbon dioxide molecule and 2 water molecules are formed. If the water vapour is condensed, additional energy will be gained due to the change from the gaseous to the liquid state, as already mentioned above. So heat from burning the natural gas as well as additional heat, which is freed during the condensation of water, are gained. The condensing boiler works with an efficiency of more than 100%. In many households water is heated using this obtained overall heat.