Some Applications of Heat 111 



The expense of installing the hot air system is less than that 

 of either hot water or steam. It takes up less space in the rooms 

 since there are no radiators. There is no danger from freezing 

 as there is no water in the pipes. On the other hand, the hot 

 air system is more or less affected by strong winds which often 

 prevent the uniform heating of a house. 



Hot Water Boilers. Many homes have hot water boilers 

 which are rilled from the water supply system. A pipe extends 

 from the bottom of the boiler to the heater and then back to the 

 boiler. As the water in this pipe is heated convection currents 

 are set up which carry the hot water to the top of the boiler where 

 it may be drawn off through a pipe leading to the faucets. 



Care of Heating Systems. In running any type of heater, 

 care should be used to keep the fire free from ashes and clinkers 

 and to spread fresh fuel evenly. Drafts should be so regulated 

 that combustion is as complete as possible, and that unburned 

 gases are drawn up the chimney. Often a thermostat is used, a 

 device which automatically regulates the heat of the house by 

 controlling the drafts. It is essential to keep sufficient water in 

 the boiler of a steam heater, to keep the expansion tank of a 

 hot water heater open, and to keep the water pan of a hot air 

 furnace filled. In freezing weather, with fires out, all water pipes 

 and boilers should be drained. 



Ventilation. Ventilation is the changing or renewing of the 

 air supply. It is closely associated with heating. The modern 

 theory of ventilation teaches that constant movement of air of 

 proper temperature, and containing a proper amount of moisture, 

 is the main thing in good ventilation. A person is more com- 

 fortable in a room having a temperature of 65 with moist air 

 than in a room heated to 70 with little moisture. 



Air contains a certain amount of moisture. This may be 

 measured and is usually expressed as a per cent of the amount 

 that the air could hold at the same temperature. If the air in a 

 room at a given time has only 50 per cent of the moisture that it 

 can hold, it is said to have a relative humidity of 50 per cent. 



Cold air will hold very little moisture, while warm air will 

 hold a great deal. When the cold air is taken from the outside 



