416 ENGINEERING ON THE FARM 



surface. If installed on catalogue rating, they will prove 

 inadequate when the thermometer stands at 20 or 30 

 below zero. 



Steam. Little need be said about steam systems. They 

 are like water systems in make-up, except that the expansion 

 tank is closed or omitted. All water is in the heater and 

 none in the radiators. There is no circulation until the 

 water in the boiler is boiling and there is pressure in the 

 pipes and radiators. This pressure, while not intended to 

 be heavy, may become so if not watched carefully. Con- 

 stant supervision is impossible in the average home. In the 

 mill, factory, or large flat building there is reason for 

 keeping a man on duty constantly, but not in the home. 



Vapor or vacuum system. The vapor or vacuum system 

 is a comparatively recent development. It is the opposite 

 in principle to the closed-tank hot- water system, as the air 

 is exhausted from the pipes and radiators and water stands 

 in the heater only, as in a steam system. The exhaustion 

 of the air makes it possible to produce steam at a tempera- 

 ture somewhat lower than 212 , which means that a small 

 fire will produce results in a few minutes, because there 

 are only a few gallons of water in the heater. It is virtually 

 a steam system and requires protective devices as carefully 

 adjusted and attended as a steam system. Furthermore, 

 leaks in the system will destroy the vacuum and it will 

 become a steam system pure and simple. 



Ventilation. It is asserted, and with reason, that special 

 ventilation devices are not necessary in the average house. 

 There is a larger air movement through walls, around win- 

 dows and doors, and up stairways than is generally realized. 

 Observations would indicate that there are from one and 

 one-half to two changes of air per hour. From this it may 

 be concluded that the only ventilating provision necessary 

 in a residence is a fireplace flue, with a damper which may 

 be closed except when the house is occupied by a large 

 number of people. 



