168 GARDENING INDOORS AND UNDER GLASS 
method does away with the greatest trouble with 
flue heating —a poor draft; for immediately the 
fire is started, the air in the chimney becomes heated, 
[, we = me eg 
Fig. 7—The best arrangement for heating a 
greenhouse by hot air, is to run a brick or 
cement flue from the furnace around under 
the benches and into the chimney over the 
fire AA—storage space; B—furnace; C—chim- 
ney; DDD—benches ; E—furnace door. 
and rising, draws the hot air from the furnace 
around through the flue with a forced draft. This 
forced draft accomplishes three other good things: 
it does away with the escape of noxious gases into 
the greenhouses, lessens the accumulation of mois- 
ture and dust from wood smoke, and distributes the 
heat much more evenly throughout the house. The 
furnace may be built of solid brick, with doors and 
grates and an arched dome, and the flue should be 
of brick for at least one-third the length from the 
furnace into the house; for the rest of the way ce- 
ment or vitrified drain pipe will be cheaper and bet- 
ter. The flue should have a gradual upward slope 
for its whole length and will vary in size with the 
