GLASS STRUCTURES. 73 



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 

 fire hotbeds. It has the merit of being easily and cheaply 

 constructed by any one 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 heating, it is probably enough to say 

 that each system has its earnest advocates and that very often 

 there is little advantage in favor of either. Where a very 

 large heating plant must be used, making a nightwatchman 

 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 re- 

 quires more radiating 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 filled with steam. It is probable 

 that an ordinary 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 radiating surface, as an ordinary dwelling house similar- 

 ly situated and enclosing the same number of cubic feet of 

 space. In estimating the amount of radiating surface neces- 

 sary it is always advisable to consult some practical person 

 acquainted with such problems. 



