When the room gets too cold, the piece of metal on the outside gets shorter and moves the arm to the left. This turns on the heating system and more fuel is burned to warm the house. The purpose of putting a thermostat into a heating system is to control temperature.
In hot climates what is important is to cool houses by sending fresh cold air through them. We can control the temperature of the rooms ad in addition dry the air and have a climate of our own making indoors. Every ice chest has a climate of its own inside it. It is strange and surprising, but true, that ice chests are kept cold by suing heat. The heat is supplied by electric power or by burning gas. Scientists tell us that before long we will be using the sun's heat to cool buildings. This will make life in hot climates much easier.
will dry dry(ies) dried