This section is from the book "The Gardener V1", by William Thomson. Also available from Amazon: The New Organic Grower: A Master's Manual of Tools and Techniques for the Home and Market Gardener.
The long sharp weather of last winter, and the immense consumption of fuel to keep up the necessary temperature to preserve my plants, caused me to ponder much about heating our horticultural buildings, and at the same time to see if it was not possible to utilise the great amount of heat which has been, up to the present time, allowed to escape up the chimney. I determined to put my ideas together, and see if I could not combine all the qualities that a boiler should possess, and the annexed engravings and the following particulars will show how I have succeeded.
The larger engraving and boiler (fig. 18) consists of nine or more separate hollow castings, placed one upon another. Upon brickwork is placed the basement or No. 1 casting, consisting of a hollow rectangular frame, into which are fixed eight (more or less, according to the size of boiler) circular hollow fire-bars, placed at such a distance from one another as to allow sufficient space for the draught.
At the back or further end of this casting are the return-pipes, and in the front the discharge-pipe for cleansing the interior of the boiler at any time. The ashpit is formed by the brickwork supporting the first or basement casting, and is enclosed by a door hung on a solid cast-iron frame, built into the brickwork or otherwise. The furnace-door is to be hung in the same way.
Upon the first casting are placed four other separate hollow castings, of which Nos. 2 and 3, forming the sides of the furnace, are fluted and placed parallel with the hollow fire-bars, and are of such a length that the two remaining castings, Nos. 4 and 5, which form respectively the back and front of the apparatus, may be flush with the ends of the first castings. The back or No. 4 casting is large enough to cover the whole or part of the end of the apparatus, and is connected at the bottom by pipes with castings Nos. 2 and 3 respectively, and at the top on each side with casting No. 11, which will be afterwards described. The front casting, No. 5, must be of such a height that the top will be level with the top of No. 6, forming the top of the furnace.
The front is built up with brickwork, with three sliding soot-doors to allow the flues to be properly cleaned out. This front or No. 5 casting is connected at the bottom by pipes with castings Nos. 2 and 3, and at the top on each side with casting No. 6. Upon the top of castings Nos. 2 and 3 is placed a sixth further and separate hollow fluted casting, forming the top of the furnace, having a space left at the back opening upwards to allow a free passage for the fire to pass out of the furnace under a separate and a hollow casting (No. 7), which, when fixed, forms flues communicating by means of other flues formed by Bimilar castings, and terminating in a rectangular opening at the top for regulating the draught, and for the passage of the smoke into the chimney.
The circulation of the water from and into every separate hollow casting is effected by means of four sets of pipes affixed externally to the castings - two sets being placed on each side of the apparatus. If desired, the crown or top casting with the flow-pipe can be placed upon No. 2 or 3 casting, and worked without the flues until required.
The flame or hot air from the fire placed on the hollow bars will pass between castings Nos. 2 and 3 until it arrives at the opening described, to be left at the back casting No. 6, where it will pass upwards towards the front through the flues formed by casting No. 7. It will then return towards the back through the flues formed by casting No. 8, again uniting and passing upwards into the flues formed by castings Nos. 9 and 10, the heat thus continuing to travel through castings Nos. 9,10, and 11 in the same way, so that the hot air will pass six times through the internal length of the apparatus before escaping into the chimney.
It will therefore be seen that this boiler is so constructed that all the caloric which the fuel contains is extracted and conveyed to the water, only just sufficient to take away the smoke being allowed to escape. Any length of flue can be added, or the boiler can be worked without any flue at all; and as the glasshouses or buildings are extended, so can heating power be added.
It requires no brickwork beyond its foundation to form the ash-pit, and a wall round, as in almost all stoke-holed, to form a frontage; the latter can, however, he dispensed with. There are no dead plates, solid bars, or bricks in this, as in most other boilers, to burn and crack, thereby admitting a quantity of cold air which tends to cool the water instead of heating it.
In order that there may be confidence in a boiler, there must be uniform strength in the castings. It is well known that the more complicated the castings, the more difficult is it to procure an equal thickness, while inequality causes unequal expansion and contraction, and occasions fractures and leakages. But in my boiler all the parts are in square sections and equally cast; consequently a regular thickness can be guaranteed. Any of the compartments can be renewed or replaced without destroying the remaining parts, as the boiler is made in sections, and is put together with leakless and durable joints - all that is necessary is a small spanned; and with this two or three ordinary labourers can dismantle and replace it in a few hours. These joints do away with all fear of fracture from expansion or contraction.
If the damper is carefully worked, it will keep up an intense heat, and the small amount of fuel required will be almost incredible; yet it will be found capable of heating a very large quantity of piping in sharp weather with less waste of heat and attention than any other boiler.
Fig. 19 shows it in sections, and how readily it can be connected and disconnected.
Fig. 20 shows that it can be worked in a similar form to the old saddle-back boiler, with the advantage of the hollow bars and the return-flue above; and the two ends can easily be added at any time by simply removing the plugs which connect them with the main part of the boiler.
Woolwich. H. Cannell, F.R.H.S.