194 



HEATING OUR HOMES 



into the glass tube, connect the tubes and fill the tank partly fullof 



water. Open the clamp. Heat the flask. 

 Observation and Explanation: Notice all changes. Describe everything 



that happens. Explain what parts of a hot- water heating system 



are represented by the 

 different parts of the ap- 

 paratus. 



The hot-water 

 heating system. - 

 In the hot-water 

 heating system, we 

 have a combined 

 furnace and boiler 

 in the cellar, radia- 

 tors in the rooms, 

 connecting pipes to 

 bring the water to 

 the radiators and 

 back to the boiler, 

 and a tank known 

 as the expansion 

 tank at the top of 

 the house, in which 

 the water may rise 



Hot-water heating system at the left, and apparatus to 

 illustrate it at the right. 



as it expands. The principle of heat transfer from the boil- 

 ers to the radiators is that of convection. The water in 

 the boiler is never heated to the boiling temperature. It 

 enters the radiators at a temperature of 175 to 185 degrees 

 Fahrenheit, and leaves it ten degrees colder. This differ- 

 ence in temperature causes the water to grow heavier, and is 

 responsible for the flow through the pipes. 



How a room is wanned by hot water. As soon as the 

 hot water reaches the radiator, heat is conducted through 



