412 ENGINEERING ON THE FARM 



pipe, C, which enters the heater at the grate level. This 

 allows for a more rapid circulation than if a single pipe 

 were used for each radiator. 



Allowance must be made for the expansion of the water. 

 This is done by means of an open tank placed in the attic, 

 or in a second-floor room above the top of the highest radiator 

 and connecting with the system at some convenient point, 

 as shown in Figure 316. The system may be filled through 

 this tank if there is no pressure system at hand. This is 

 called the open- tank hot- water system. If the tank D, in 

 Figure 316, were capped tight, and little or no water 

 reached the tank, there would be a quantity of air confined 

 which would be compressed, because the water in the heater, 

 pipes, and radiators expands when heated. This is the 

 closed-tank or semi-steam system. The advantage is a 

 higher temperature of the water before the boiling point 

 is reached. The higher temperature will allow smaller 

 pipes and smaller radiators, and the practice is to install a 

 smaller heater also. The cost of installation will be less 

 in consequence. The objection to this semi-steam system 

 is the need of safety devices, which may fail, and harder 

 firing, which requires more fuel. 



Hot-water pipes. A hot- water system may be installed 

 with the most economical results after the house is built, 

 for then the pipes are all exposed and add to the heating 

 surface in the room. It may be put in when the building 

 is being erected, as shown in Figure 317, where all pipes 

 are concealed in the partitions. Never conceal a pipe in 

 an outside wall; too much heat is lost. All pipes should 

 be so placed that there are no pockets or traps in them, 

 and the return pipes should lie just a little below the corre- 

 sponding feed pipe. This system will work without this 

 precaution, but will work better if it is observed. A radia- 

 tor with less than 40 square feet of surface should have a 

 1 -inch pipe; one with from 40 to 80 square feet, a i>^-inch 

 pipe; and one with from 80 to 125 square feet, a i^-inch 



