nd 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 cement or vitrified drain pipe will be cheaper and
better. The flue should have a gradual upward slope for its whole length
and will vary in size with the house to be heated, from five to eight
or nine inches in diameter, the latter being sufficient for a house 60
by 21 feet. The flue should be raised a little from the ground, and at
no point should any woodwork be nearer than six inches to it. Very small
houses, especially if not started up until January, may be heated by an
ordinary wood stove with the stove pipe run the length of the house, but
such an arrangement will give off a very drying and uneven heat, and
require a lot of attention, to say nothing of its danger.

[Illustration: Fig. 8--Hot water is undoubtedly the most satisfactory
method of heating the small greenhouse. The diagram shows a 1-1/2-inch
supply pipe leading out from the boiler, with 1-inch returns under the
benches, making a satisfactory system for the lean-to type described in
detail in the previous chapter.]

[Illustration: Fig. 9--For the larger greenhouse of the isolated
double-slope type, 21 x 50 feet in size, a 2-inch supply pipe, with five
1-1/2-inch returns under the outer benches, will secure a temperature of
55 degrees.]

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 of the diagrams is shown an arrangement of pipes
for heating a house 21 x 50 feet, and in another piping for lean-to
described in the preceding chapter. With the small pipe sufficient for
such a house as that illustrated in the latter 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, say one
inch in ten feet, from as near the heater as practical. For all this
work second-hand piping, newly threaded, will answer very well, and it
may be bought for about four cents per foot for one-inch pipe; six cents
for one and one-half inch, and eight cents for two-inch. In putting the
stove or heater in place, it should be sunk below the level upon which
the pipes will run, and attention should also be gi