Greenhouse Heatin 



cient, safe, and economical. The inlet should be in the bottom, at the 

 rear end. The hole should be large, and reinforced with a wrought flange, 

 riveted on. The outlet should be of the same size as the inlet, and situated 

 in the top, as close to the front end as practicable. In this case there is a 

 natural flow of water from the inlet at the lower end of the boiler to the 

 outlet at the upper end ; a natural rising of the expanding water through 

 an unobstructed space, with an easy flow, like the current of a river. In 

 all the other types this flow is more or less obstructed. 



Practical tests made to ascertain the amount of friction in different 

 types of boilers have demonstrated that the horizontal tubular boiler, set 

 as above described, with a carefully-designed radiating system, will respond 

 readily to hard firing, and show at high temperature a difference of not 

 more than three degrees Fahr. between the outward flow and the return. 

 The writer has never been able to get anywhere near as good a result in 

 any sectional or firebox boiler. The florist seeking a hot- water heater can 

 make no serious mistake in selecting any one of the three boilers described, 

 as all do good work. 



The Closed or Perkins Method 



We will now consider the third system of hot-water heating, namely, 

 the so-called closed, or Perkins method. This differs from the other two 

 alluded to above by having an increased pressure. In this system, which 

 is sealed tight, the usual installation includes an expansion tank filled with 

 air. After the apparatus has been fired sufficiently to expel all the air from 

 the water, the entire apparatus is sealed air-tight. The air in the expan- 

 sion tank provides an elastic medium which allows for expansion of the 

 water contained, when heated. There is but one point gained — if it be a 

 gain — and that is, the increased pressure will allow of a higher water tem- 

 perature in the radiating coils. The entire apparatus is vulnerable to leaks, 

 and in practice is very complicated, and there would seem to be no excuse, 

 or reason, for its employment by florists. The second system described will 

 allow of a water temperature of 212 degrees and over. Few florists care 

 for more. 



The Pump Method 



Before passing the subject of hot-water heating it may be interesting 

 to mention another type of apparatus which may be adapted to such installa- 

 tions. I allude to a system in which the circulation of hot water is impelled 

 by mechanical force, such as a steam or belt-driven pump, which may be 

 operated either by an engine, an electric motor, or a water motor. In the 



iSo 



