METHODS OF HEATING 351 



in. in 10 ft., so that the water will flow out of the system as 

 quickly as possible. A low place or sag in the pipes or heat- 

 ing coils may trap the water. The result will be that a noisy 

 snapping or hammering will take place when steam is turned 

 on. 



The pipe coils are hung on rollers to allow for expansion. 

 After the first heating season in a new building, and occasion- 

 ally in all buildings, the piping system should be examined. 

 The shrinkage and settling of doors may throw pipes and 

 radiators out of place sufficiently to cause serious trouble in 

 the action of the system. 



The rule for finding the size of the main steam pipe is: 

 Divide the amount of the direct heating surface in square 

 feet by 100; divide the quotient by .7854; then take the 

 square root of this last quotient. The result will be the 

 diameter of the pipe in inches. (Pipe area = -^ of 

 heating surface.) 



395. Risers and Returns. Risers are the pipes that pass 

 from the lower floor to the upper floors and to which the 

 radiators are connected by short pipes or nipples. These 

 connections must allow for expansion, and it is advisable to 

 put a valve into the lower end of every riser. By taking the 

 steam from the top of the main, less water enters the riser. 



Returns are the pipes that receive the water of condensa- 

 tion from the coils and conduct it back to the boiler room. 



396. Steam and Air Valves. A heating system, when 

 cold, fills with air by leakage around valve stems. This air 

 must be allowed to escape so that steam may enter. Auto- 

 matic air valves may be placed on every radiator and coil. 

 These valves are open when cold. As steam enters the sys- 



