GLASS STRUCTURES. 



77 



putting in and taking out the manure. The use of stable manure 

 to supplement the heating apparatus is a practice that may be 

 economically followed in locations where coal is high priced and 

 stable manure abundant. The heating arrangement could be 

 either steam or hot water with the flow pipes high up near the 

 roof, as shown at A and B and the returns at C and D. 



Methods of Heating. — There are practically three methods of 

 heating greenhouses, viz.: by smoke flue, by hot water and by 

 steam. Heating by smoke flue is described under the head of 

 flre hotbeds. It has the merit of being easily and cheaply con- 

 structed by anyone having some little ingenuity. Even when 

 made on the best principles it is probably more wasteful of fuel 

 than a good steam or hot water apparatus, but where inferior 

 fuel can be cheaply obtained a smoke flue may often be used 

 to advantage. As for the relative merits of hot water and 

 steam apparatus for healing, it is probably enough to say that 

 each system nas its earnest advocates and that very often there 

 is little advantage in favor of either. Where a very large heat- 

 ing plant must be used, making a night watchman necessary, it 

 is best to plan for steam heating at low pressure. For small 

 greenhouses perhaps a hot water plant is best. It costs more to 

 put in the hot water apparatus because it requires more radi- 

 ating surface since the pipes are not heated as hot as when 

 steam is used. Some exclusive merits are perhaps justly claimed 

 for a combination of hot water and steam, in which system hot 

 water is used for heating in mild weather, while in severe 

 weather the water is lowered in the boiler, a regulator is put on 

 and the pipes are fllled with steam. It is probable that an ordi- 

 nary tubular steam boiler is the most practical kind to use 

 either for a hot water or steam heating apparatus. 



The amount of radiating surface necessary for heating a 

 greenhouse will depend on the temperature to be maintained and 

 the location of the house. In a general way, one should figure 

 that glass houses will require at least four times as much radi- 

 nting surface as an ordinary dwelling house similarly situated 

 and enclosing the same number of cubic feet of space. In 

 estimating the amount of radiating surface necessary it is always 

 advisable to consult some practical person acquainted with such 

 problems. 



V 



