This section is from the book "The Principles And Practice Of Modern House-Construction", by G. Lister Sutcliffe. Also available from Amazon: How Your House Works: A Visual Guide to Understanding & Maintaining Your Home.
In the United States, Smead's system of heating by hot air has been very widely used in public schools and other buildings, and is stated to have given great satisfaction. Before describing this system, I shall borrow from Mr. Smead's work on the subject five illustrations (figs. 484 to 488), showing the results of various arrangements for the entrance and exit of the air. In Fig. 484 the heated air enters through a grid, fixed in the middle of the floor, the result being that a column of heated air rises in the middle of the room and passes away near the ceiling, leaving a stagnant mass of cold foul air. The arrangement in Fig. 485 is very similar. That in rig 486 shows a slight improvement, while fig 487 shows direct displacement of all the cold sir by the warmed sir, and Fig. - 488 shows an additional improvement by using a number of outlets at the floor-level, and then passing the foul air out between the floor of the room and the ceiling of the room be1ow. It will be observed that no account is taken of the fact, that the products of combustion of the gas in the ordinary way would be taken down to the breathing-level.
Fig 488. - The "Smead" Furnace.
In my opinion, there are several objections to the Smead system. One is that the products of respiration, and emanations from the body, which would naturally pass upwards (as they leave the body at a temperature of 98° Fahr.), are carried downwards in the current of air to the outlet near the floor, and the sir thus vitiated must be breathed over again. which is undoubtedly a bad feature. The second objection is that, in order to keep a room warmed to
(say) 60° or 65° Fahr., the incoming air must necessarily be at a much higher temperature, probably about 120° Fahr. This current of heated air is most objectionable to any person standing or sitting near the inlet; but this latter objection is not confined to the Smead apparatus, but is common to all systems in which heated air is relied upon as the sole means of wanning the rooms.
The Smead apparatus consists of a special type of air-heating furnace, and a system of inlet and outlet flues. The furnace is shown in Fig. 489, which represents a type which has been gradually perfected from a much inferior form. The heater itself is inclosed in brick walls, which form a complete box round it. and it is placed as shown in the perspective view, Fig. 490. The furnace is built in a special fresh-air room provided with large inlets from outside. The cold external air enters this room, and is drawn through the openings in the brickwork around the heater; it rises over the highly-heated iron surfaces of the heater, and then passes up the wall-flues to the different rooms. As a rule, one flue is arranged for each room, so that trouble may be avoided from baffling.
Fig. 490. - View of "Smead" Furnace let In Brickwork.
The system of inlets is very clearly shown in Fig. 494, from which it will be observed that the inlet-flue is carried up a little above the floor-level, and is stopped there; the outlets are in each case close to the floor, in the wall opposite the inlet, as shown in Fig. 491, and communicate with the upcast shaft. In plan the shafts are arranged as shown in Fig. 492. The smoke-flue is next the ventilating shaft, so that the latter is kept constantly hot; they should be carried to a height above the roof of the building, sufficient to ensure freedom from the baffling caused by conflicting currents.
Fig. 491 - General Arrangement of lulets and Outlets in the "Smead" System.
The arrangement for the regulation of heat is very ingenious. A view of the register and regulator, as seen from the interior of the room, is given in Fig. 493. It will be seen that the register is designed to give the maximum amount of opening possible, and is of very ample size, so that the current of air entering may be of low velocity. Just above the register is plaeed the regulator, marked for warm air and cold air, and any desired mixture can be obtained by means of a very simple and effective valve, which is shown in Fig. 494.
It is quite obvious that if the Smead system of heating is to be applied a, b. warms air to first story: c, d, warm air to second story; e, f, warm air to third story; g, smoke successfully to a building, that building must be originally designed for it The system has been very largely used in the United States, and appears to have there given great satisfaction. A very elaborate work has been published by the Isaac D. Smead Company of Toledo, which is full of coloured plates. The book is well worthy of careful study. The system appears to be very economical in the consumption of fuel, and there can be no risk of explosion as is the case with the use of hot-water and steam plant. The incoming air is not, as a rule, washed or screened in any way. and is passed into the rooms at a temperature of about 120° Fahr. I am not aware that the air is humidified; no mention is made of this in the work alluded to. It is, however, obvious, that to heat air at even freezing-point up to 120° Fahr., without adding to it the requisite amount of moisture, must render the atmosphere in the rooms very dry, and in some cases this may be found objectionable. The mere heat of the incoming air will also probably be found uncomfortable to a person placed near the inlet, although it must always be borne in mind that air at such a temperature, or even higher, will rise in the vicinity of a close stove, and if the current of air passing over a hot-water or steam radiator be slow enough, the air may acquire a temperature considerably higher than that of the general body of air in the room.
Fig. 492 - Plan showing stack of inlets and outlets, "Smead" system.
Due, h, ventilating shaft.