192 GREENHOUSE CONSTRUCTION AND HEATING. 
A coil of lin. piping, with four laps, will heat up to 
100ft. of 4in. piping easily, and being fed from the top, 
the fire is easily managed, and will keep alight for eight 
or ten hours. At the present time, I have one, of liin. 
tube, which heats 150ft. of 4in. piping, and a house 50ft. 
by 11it., capitally, while a double flue, carried from the 
furnace across one end of the house and back, affords 
plenty of heat for a covered propagating bed as well. 
This is a capital plan, especially with boilers of this class, 
as utilizing a lot of surplus heat that would otherwise 
pass away up the chimney and be wasted, and rendering 
the apparatus a fairly economical one, on the whole. 
Such a coil only costs from 15s. to 20s., or a larger size 
25s., so that this is by far the cheapest and best kind of 
boiler for the working man or mechanic’s small greenhouse. 
Any handy man can set a coil sufficiently well, and only 
some 500 or 600 of bricks are required. 
The circular part of the furnace above the coil may 
be carried up a foot or more, and this forms a kind of 
hopper to contain a reserve of fuel; in this case the 
interior should be rendered as smooth and even as possible. 
Or a short chimney-pot may be fixed on the top, with 
a lid, for the same purpose. 
We now pass to the class of independent boilers, which 
require no brickwork setting, but merely to be stood on 
a few loose bricks at any convenient point, and connected 
on to the pipes. At the same time all such boilers are 
the better for a casing of brick or some other non- 
conducting material, which not only conserves the heat, 
but protects the metal from injury by the weather, etc. 
Though extremely useful for small structures with lengths 
