228 FUEL AND HEATING 



The position of the boiler is very important. Choose 

 a location that will be central even if additions have to 

 be made to the establishment. It must also be accessible, 

 and if located in a boiler house this should not be so placed 

 as to cast a shadow over the greenhouses. The smoke- 

 stack should likewise not be in a position to throw a 

 shadow, and if at all practicable should be away from the 

 direction of the prevailing winds, otherwise smoke and 

 soot will be thrown over the glass. A stack lo in. in 

 diameter is suggested by expert heating engineers for 

 anything below a lo h. p. boiler. If a 50 h. p. boiler is 

 used a 20 in. diameter should be built. The height of 

 the stack will vary between 25 ft. if soft coal is burned, 

 and 50 ft. for hard coal. 



Steam is employed in all places over, say, 40,000 or 

 50,000 sq. ft. of glass. If hot water is used, the force 

 system is preferable to the gravity system; excavations 

 for the boiler are then seldom necessary, thus saving labor 

 and expense. With the steamtrap system some dip or 

 excavation would be essential in order to catch the water 

 of condensation. 



As to boilers, it is important that these have a deep 

 fire box, that is, deep from the top to the grate, so that all 

 the gases from the coal may be properly consumed. Auto- 

 matic draught regulators are advisable. Sectional boilers 

 are excellent inasmuch as they can be added to as the 

 area of glass increases. In any case, the most efficient 

 boilers are those that give the longest passage for the 

 heat, flames, or burning gases over the water area, or 

 tubes of the boiler. Thin waterways are quickly heated, 

 but they must, of course, be strong enough to last a reason- 

 able time and prevent bursts. Sectional boilers should be 

 covered with asbestos. 



