This section is from the book "Modern Buildings, Their Planning, Construction And Equipment Vol3", by G. A. T. Middleton. Also available from Amazon: Modern Buildings.
A considerable number of years ago Dr. Arnott introduced a grate which amounted to being a fire-box sunk in the hearth, or equivalent to this, so that no air came to the fuel except at the top. While in this state the grate afforded a little heat, but the remarkable result was that the boxed-in fire, instead of going out, was found to keep alight a great number of hours without attention. When warmth was needed it was only necessary to uncover a part of the front of the fire (which he did by winding the fire-box up) and the fuel quickly commenced to burn briskly. This is the principle and effect of the Eagle grate when arranged as shown at D. The makers state that the fire can be kept alight for 14 hours without attention, but the writer has had it do so for 18 hours, and at the end of that time the fire was red and of quite a good appearance. It seems as if combustion could be stayed, as the fire was not made up above the top front bar, the fire-box not holding more than a few small shovels of coal.
Of recent years there has been a tendency to do away with the front bars of grates, so that no barrier, however slight, shall exist between the fire and the room. Impetus was given to this by the introduction of the Well-fire, an illustration of which is given in Fig. 91. This, as will be seen, much resembles a Teale grate, but without front bars, and it has a raised hearth, with an air flue in it, as the economiser. The raised hearth is not needed when the "well" can be sunk in the ordinary hearth, but this is not always possible on floors above the ground floor. If the preceding pages have been read it will be readily seen that the grate has a high effectiveness, and, to the majority, the piled fire and absence of bars has a pleasing effect.
The success of the well-fire has brought into existence a number of grates designed to work without front bars, and now commonly designated sunk or basket fires. These do not necessitate a raised hearth, though the effect of this is sought after. Fig. 92 shows such a grate, one of Barnard, Bishop & Barnard's. The economiser in this case is made as a hit-and-miss ventilator, so that in regulating the speed of combustion the economiser itself need not be bodily shifted.
Fig. 93 illustrates a grate of similar character, but having a front bar which can be raised to afford support to the fuel when a large fire is needed; or lowered, as illustrated, to form a trivet; or it can be pushed back beneath the bottom bars and so make the grate barless. There are now numbers of such grates on the market, and the few examples given are merely to afford an idea of the progress that has occurred in this industry.
A grate worthy of notice, as affording all the effective appearance of the dog-grate but without its faults, is the "Nautilus," an example of which is given in Fig. 94. This grate is intended to stand in a tiled opening, but instead of the smoke getting away up the open mouth of the chimney above, this latter opening is closed and the grate nozzle (at the back of the grate) is connected to a flue brought down in the wall at the rear. The grate being on wheels is to admit of its being drawn forward when the sweep has to clean the flue and chimney.
Ventilating Grates It is somewhat surprising that the ventilating grate has not come into more general use, remembering that, apart from the question of ventilation, it largely obviates that fault of the ordinary grate, the cold draughts induced. It is quite recognised that with every grate there has to be a chimney, and that this chimney extracts air from the room in great volumes (doing excellent work as an extract ventilator in this respect). This being so, a moment's thought will show that the extracted air must be replaced from - somewhere. In the ordinary way it comes through doorways, if the doors are open, otherwise through crevices around doors and windows. In practically every case it comes from a cold source and is then known as a draught, which everything possible is done to exclude. The correct thing would be to encourage this air movement, as the chimney needs a good supply and the occupants of the room cannot have too much air for health, if it is not cold enough to lower temperature and vitality seriously.
The ventilating grate meets this condition very successfully, as it provides for a good sized clear hole being made in the room wall, and the air coming through this aperture is warmed, and consequently does not manifest itself as a draught. The provision of the hole, it will be seen, instantly checks, often quite disposes of, the draughts from other sources, for it follows that air will not flow through circuitous and confined ways, if all that is needed can come direct through a hole in an outer wall. This can be tested by opening a window, which instantly stops the draughts through door crevices. The warming of the in-flowing air does not impede its flow to a noticeable extent, as will be seen by Fig. 95, which shows the chief parts of a ventilating grate in plan and section. The grate is of a type that projects on to the hearth (a type that is too much neglected), and around the soundly made fire-box is an air-chamber which is airtight except for the inlet aperture at bottom and the grated sloping casting which forms the top of the air chamber. The gills forming so many air flues and the metal being hot, the air cannot get through and escape into the room without being agreeably tempered if not fully warm. The peculiar effect obtained with gilled surfaces, the extension of surface so obtained, and the reduction in the general temperature of the surface, has been already spoken of.
Perhaps the best known ventilating grate is that made by Shorland of Manchester, a section of which is given in Fig. 96. This is a grate interior with air-chamber behind, and the special feature is the arrangement for discharging the air. Instead of coming through a grated panel in the air chamber, a nozzle is provided for a warm-air duct to be taken vertically and discharged at a high point in the room wall as shown. This agrees with the generally accepted opinion that warm air should be discharged high, and vitiated air extracted from a low point, the openings for both to be on the same wall, as explained in the Chapter on Ventilation.