170 GARDENING INDOORS AND UNDER GLASS 
By far the most satisfactory way will be to use 
hot water. If the size of the house will not justify 
the purchase of a small heater —a second-hand 
one may often be had at a very reasonable figure — 
a substitute may be had by inserting a hot-water coil 
in a stove or in the house furnace. In one 
Fig. o—For the larger greenhouse of the 
isolated double-slope type, 21 x 50 feet in size, a 
2-inch supply pipe, with five 14-inch returns 
under the outer benches, will secure a tem- 
perature of 55 degrees. 
of the diagrams is shown an arrangement of 
pipes for heating a house 21x50 feet, and 
in another piping for lean-to described in 
the preceding chapter. With the small pipe suf- 
ficient for such a house as that illustrated in the lat- 
ter diagram, the work can be done by anyone at all 
acquainted with the use of pipe tools; if possible, 
the pipes should be given a slight downward slope, 
