Of these there are many varieties on the market - all sorts, shapes, and sizes. Some of the older types, like the "wedge", "coil", and "conical", have been driven out altogether, even from private establishments, having been superseded by the "saddle" (of various designs), the upright and horizontal "tubu-lars", the "Cornish" or cylinder boiler. And during recent years the "sectional" boilers largely used on the Continent and in America have begun to find a footing amongst British growers.

What the market grower and nurseryman aims at above all things is to have a boiler that will not only wear well, but will generate the greatest amount of heat at the least expense of coal or coke, or labour in stoking. In addition to this, one that can be repaired easily is a great advantage.

At the present day perhaps the horizontal tubular boiler, as shown in fig. 171, is the most popular with large growers. The flues are in a direct line to the smoke shaft, a greater surface is exposed to the fire and consequently heat is generated more quickly; and in the event of a tube giving way a new one can be substituted in a very short time. A boiler of this description, 9 1/2 ft. long, is capable of heating 2000 ft. run of 4-in. pipe, the total cost for boiler and fittings being about 20.

The duplex upright tubular boiler as shown in fig. 172, although extensively used in private places, is not so largely patronized by big market growers. This particular boiler is made in two equal parts each of which can be worked independent of the other in case of accident. As a rule the two sections are worked as one boiler, and this gives the advantage of two flows and two returns, which can be made independent of each other if necessary.

Rochford Horizontal Tubular Boiler.

Fig. 171. - Rochford Horizontal Tubular Boiler.

Weeks's Duplex Upright Tubular Boiler.

Fig. 172. - Weeks's Duplex Upright Tubular Boiler.