GLASS STRUCTURES 109 



hot-water is used for heating in mild weather, and 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 a steam heating apparatus. 



The amount of radiating surface necessary for heat- 

 ing 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 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. 



MISCELLANEOUS MATTERS CONNECTED WITH THE BUILD- 

 ING AND CARE OF HOTBEDS AND GREENHOUSES 



The sash for hotbeds or cold frames should be about 

 3x6 ft. or 4x4 J/^ ft. in size; the glass free from blisters, of double 

 strength, and lapped not more than one-fourth of an inch. 

 If lapped more than this, water is liable to freeze the laps and 

 crack the glass, and dirt will collect between the glass. It 

 should be bedded in putty and nailed in, not puttied in. 

 Common window sash might be used for the purpose in a 

 small way and temporarily, but it is not strong enough to last 

 well; and besides as the sash bars run both ways and 

 project beyond the glass the rain water cannot run 

 off, but soaks the wood and leaks through into the 

 hotbed, making it too wet in places. Also, the cross bars 

 in common window sash make a needless extra shadow 

 that is objectionable. Regular hotbed sash is made with 

 sash bars running only one way so that the water 



