This section is from the book "Spons' Mechanics' Own Book: A Manual For Handicraftsmen And Amateurs", by Edward Spon. Also available from Amazon: Spons' Mechanics' Own Book.
This subject has been most ably discussed by Dr. Pridgin Teale, in connection with the economising of fuel in house fires. His remarks will well bear repeating.
"It is hardly possible to separate the 2 questions of economy of fuel and abatement of smoke. None who, in their own person, or as the companion or nurse of friends and relatives, have gone through the miseries of bronchitis or asthma in a dense London fog, can fail to perceive that this is a serious medical, not less than a great economical, question. Nine million tons of coal - one-fourth of the domestic fuel consumption in this kingdom - is what I estimate as a possible reward to the public if they will have the sense, the energy, and the determination to adopt the principles here advocated, and which can be applied for a very small outlay. Much has been said by scientific men about waste of fuel, and strong arguments have been advanced which make it probable that the most economical and smokeless method of using coal is to convert it first of all into gas and coke, and then to deliver it for consumption in this form instead of coal. Theoretically, no doubt, this is the most scientific and most perfect use of fuel, and the day may come when its universal adoption may be possible. But before that time arrives many things must happen.
The mode of manufacture, the apparatus on a mighty scale, and the mode of distribution must be developed, nay, almost created, and a revolution must be effected in nearly every fireplace in the kingdom. At present its realization seems to be in a very remote future. Meantime I ask the public to adopt a method which is the same in principle, and in perfection not so very far short of it. It is nothing, more nor less, than that every fireplace should make its own gas and burn it, and make its own coke and burn it, and this can be done approximately at comparatively little cost, and without falling foul of any patent, or causing serious disturbances of existing fireplaces. We must, first of all, do away with the fallacy that fires won't burn unless air passes through the bottom or front of the fire. The draught under the fire is what people swear by (aye, and many practical and scientific men too), and most difficult it is to sweep this cobweb away from people's brains. They provide 2 or 3 times as much air as is needed for combustion, 1/3, perhaps, being the necessary supply of oxygen, the remainder serving to make a draught to blow the fire into a white heat, and to carry no end of waste heat rapidly up the chimney; 2/3 of cold air chilling the fire, 2/3 more than needful of cold air coming into the room to chill it; and much of the smoke and combustible gases hurried unburnt up the chimney.
The two views which I am anxious to enforce upon the attention of the public, of builders, of ironmongers, and of inventors, are these : that the open grating under the fire is wrong in principle, defective in heating power, and wasteful of fuel, and that the right principle of burning coal is that no current of air should pass through the bottom of the fire, and that the bottom of the fire should be kept hot. This principle is violated by the plan of closing the slits in the grate by an iron plate resting on the grate, which cuts off the draught, but allows the chamber beneath the fire to become cold, and when cinders reach the plate they become chilled, cease to burn, and the fire becomes dead. The right principle is acted upon by the various grates with fire-brick bottoms, and the English public owes much to the inventor of this principle as carried out in the Abbotsford grates, which have done much to educate the British public in the appreciation of the fact that a fire will burn well with a current of air passing over it, and not through it. But there is a better thing than the solid firebrick bottom, and that is a chamber underneath the grating, shut in from the outer air by a shield resting on the hearth and rising to the level of the bottom bar of the range.
This hot-air chamber, into which fine ash can fall, produces on the whole a brighter and cleaner fire, and one which is more readily revived when low, than the solid fire-brick. There is another mighty advantage in the principle of the "economiser" - an unspeakable advantage, it is applicable to almost every existing fireplace, and it need not cost more than 3-4s. This idea has now been long on its trial. It has been applied in hundreds of houses. It has been submitted to the very severe test of being applied to an infinite variety of grates, under a great variety of circumstances, and tried with coke, anthracite, and coal, good, bad, and indifferent. The effect has been, in an enormous number of instances, a marked success in saving coal and labour, and in more comfortable uniform warmth to the room. The failures have been very few indeed. I have drawn up 7 rules for the construction of a fireplace, all of which are pronounced to be sound : - ■
1. As much fire-brick, and as little iron as possible.
2. The back and side's of the fireplace should be fire-brick.
3. The back of the fireplace should lean or arch over the fire, so as to become heated by the rising flame.
4. The bottom of the fire or grating should be deep from before backwards, probably not less than 9 in. for a small room nor more than 11 in. for a large room.
5. The slits in the grating should be narrow, perhaps 1/4 in. wide, for a sitting-room grate, 3/8 in. for a kitchen grate.
6. The bars in front should be narrow.
7. The chamber beneath the fire should be closed in front by a shield or economiser. "There is one caution which should be given. There is no doubt about the fact that immediately beneath the fire the hearthstone is hotter, and the ashes remain much hotter when the 'economised is used. This may increase the risk of fire whenever wooden beams lie under the fireplace. In any case of doubt, the best plan would be to take up the hearthstone and examine, and relay with safe materials; but should this be impossible, safety may be secured by covering the hearthstone with a sufficient thickness of fire-brick, just within the space enclosed by the 'economised - leaving a space of 2 or more in. between the fire-brick hearth and the bottom of the fire. In lighting the fire, if there be no cinders on which to build the fire, it is well to draw away the 'economiser' for a short time until the fire has got hold; but, if there be cinders left from the previous day, on the top of which the paper and wood can be placed, then the fire may be lighted with the ' economiser' in its place. There is a great art in mending a fire. It is wasteful to throw lumps of coal higgledy-piggledy on a fire.
The red embers should be first broken up so as to make a level surface, then pieces of coal should be laid flat on the fire and fitted in almost like pavement; lastly, if the fire is intended to burn slowly and last very long, small coal should be laid on the top. An 'economised' fire so made will, in a short time, heat the coal through, and give off gases, which will ignite and burn brightly on the surface of the black mass, and when the gases are burnt off there is a large surface of red-hot coke."
The annexed illustrations show the application of the economiser. Fig. 1391 is a kitchen range, a being the economiser and b the front damper. The latter should always be used in warm weather, unless the front of the fire is needed for roasting, and should be put on at night. Fig. 1392 is a bedroom fireplace having fire-brick sides a, fire-brick back b leaning over the fire, narrow front bars c movable, grating d with narrow slits, chamber under the fire closed by economiser e, and front damper f which can close the lower § of the front of the fire at night or when a slow fire is needed.
The "economiser" is a shield of sheet iron which stands on the hearth, and rises as high as the lowest bar of the grate, against which it should fit accurately, so as to shut in the space or chamber under the fire. If the front of the range be curved or angular, as in most register stoves, the economiser will stand, owing to its shape - but if the front be straight, the economiser needs supports such as are shown. "Ordinary economisers" are made of 16-gauge charcoal iron plate, with 3/8-in. bright steel moulding at the top, 1/2-in. moulding at the bottom, and 1 or 2 knobs as required. "Kitchen economisers" are made of 16-gauge iron, with 1/2-in. semicircle iron at the top edge; and with supports in scroll form of 1/2-in. semicircle iron. Some makers use rather thinner iron plate and give strength by the mouldings. Some have used too thin plates, little better than tin, which have warped and so become more or less useless. Great care should be spent in taking the dimensions - as every grate has to be measured - as a foot for a boot. This renders it almost impossible to send orders to a maker by post. Some skilled person must take the measure, and take it accurately. The dimensions to be taken are; firstly, the outline of the bottom bar of the grate.
If it he curved, or angular, the outline can be well taken by a piece of leaden gas-pipe, which, moulded to the outline, can then be traced upon paper or carried carefully away to the makers; secondly, the height must be measured from the hearthstone to the bottom bar. This is the "econo-miser" in its simplest and cheapest form, as applicable to nearly every ordinary range.
Ornament can be added to taste. It is obvious that the adaptation of the econo-miser need not displace the old-fashioned ash-pan, and that the 2 can be combined, or that the economiser may be made like a drawer and catch the ashes. All such variations will work well provided that the main principles be adhered to of cutting off the under current," and " keeping the chamber under the fire hot." But the simplest form is the best.
Fig. 1393 illustrates a few typical specimens of modern improved open grates devised to increase the radiation of beat and perfect the combustion of the fuel: A is a combination of Parson's grate and economiscr with a Milner back; B is Nelson and Sons' "rifle" back; C is a Galton back; D, Jaffrey's grate.