CHAPTER VII.

WARMING.

(50) General Principles of Warming Rooms.

THE nervous system is benumbed by great heat or cold.

Humboldt long ago drew attention to the analogy between the torpor of the larger reptiles during tropical heat and the hybernation of certain animals during winter.

Cold lessens the vitality generally, its stress being most felt by the aged and young; the heat in this country is seldom excessive for a sufficiently long period to cause disturbance to the public health, save indirectly.

The best temperature for intellectual activity is from 62° to 65°, therefore these are the temperatures for living rooms; on the other hand sleeping rooms are best kept much cooler; sleep is generally soundest when the air of the room is a few degrees above freezing point, always provided that the body itself is kept warm by sufficient wraps; it is a great mistake to heat in any way sleeping rooms, that is provided the sleepers are in good health.

The difficulty of maintenance of temperature to any particular degree can hardly be exaggerated. Our houses are as it were little cellular boxes, at the bottom of a vast aerial ocean, which is often more than 20° in excess or below the temperature desired. Nor does it make the practical solution of the problem easier when we have to build the same house for extremes of heat and cold.

(51) Warming by Open Fireplaces.

The "pleasant pokeable fire," as an open fire has been called, is peculiarly English; countries like Sweden, Norway, Russia, and

the Northern States, with their extreme winters, have preferred the more economical stoves.

The open fire is of course wasteful: a pound of coal, if all its heat were utilized, would warm a room 20 feet square and 12 feet high 10° above the surrounding air, but quite eight times that quantity has to be used in open grates even of the best construction. On the other hand they have two great merits, they are cheerful and powerful ventilators: most chimneys of ordinary houses extract from 30,000 to 40,000 cubic feet of air hourly.

The best modern grates are of the warm air type, that is cold pure air is conveyed from without by a special flue to the back of the grate, it is then warmed by contact with the heated surfaces and streams into the room,

The following are the principles to be observed in the construction of warm air grates. The bars in front should be as thin as possible, and fitted not horizontally but vertically, the sides of firebrick, and splayed to an angle of 135°. The back and sides of the grate should be “gilled," the gills projecting into the chamber at the back. The flue leading to the back of the grate must draw its air supply from an unexceptionable source. The warm air must be delivered at the lowest practicable point, the usual place being just below the mantel-board. The grate itself should be raised a few inches above the floor, and if slow combustion is required, the bottom of the grate may be formed of a solid bit of terra-cotta or fire-clay. In places where instead of coal, wood is burnt, the fuel may be on the hearth itself; in that case the air chamber should not alone be at the back of the fire-place, but should communicate also with a space under the hearth; by means of this "hollow hearth," the heat which otherwise would be expended on the stove and ground is in great part conveyed into the room.

(52) Stoves.

The old fashioned stove, which may be defined as a sheet-iron box in which the fuel was burnt, and connected with a pipe to lead away the smoke and gases, was an efficient but unhealthy method of heating a room. When in full action a length of the pipe, and no small portion of the stove itself would be heated to redness, the thin iron in that state became of a spongy texture, and carbon monoxide and dioxide freely streamed through, poisoning

the atmosphere. The little floating particles of organic matter in the air would be borne by currents against the red-hot iron and be consumed. The effect of these miniature cremations, small at any given point or moment, was considerable when the process went on for hours and caused the air to feel "burnt and dry," and to have a peculiar smell. The Pensylvanian stove invented by Franklin, was one of the earliest built on correct principles; the modern ones are little more than improvements of this type of

stove.

The first principle of a modern stove is that it shall be constructed of materials which will not permit the transmission of gases through the walls; this is attained by the use of fire-clay linings. The stove should be composed of a judicious combination of iron, fire-clay, fire-brick or porcelain. The forms of stoves are so varied that only types of the chief can be described.

Slow-combustion Stoves.-The Meidingen stove is much used in Germany, it is composed of an inner cylinder made up of a series. of thick externally fluted rings; the rings are enclosed with a double casing, which casing can be connected with the outer air by means of a pipe. A door fixed in the grate regulates the draught, and when the stove is fully charged the fuel may be made to burn quickly in from three to four hours, or slowly in twenty-four hours, according to necessity.

A slow combustion stove to which was awarded a gold medal at the International Health Exhibition is constructed as follows: The fire-place is lined with fire-clay, there is a door for the reception of the fuel, and there is another door at the lower part of the stove serving the double purpose of admitting air and removing the ashes. The gases of combustion and the smoke, instead of escaping direct into the chimney, are first ignited and then made to pass through two chambers, and they finally escape through the flue; between the divided chamber and the fuel box is another chamber, the office of which is to warm the air supplied to the room. To this chamber a special flue carried underneath the boards conveys the outside atmosphere and it enters the room as warm air. The stove is essentially a slow combustion stove, and is an improvement upon those which are directly supplied with air from outside, for these of course do not ventilate the rooms, because most of them are entirely closed.

Saxon Snell's Thermohydric Grate.-This is more a stove than a grate, combining however the advantages of both. A small boiler is placed behind the grate and communicates with a series of iron pipes alongside of it. These are also filled with water and air is admitted to the room between these hot water pipes. The products of combustion are carried off by a flue, which as may be seen in the St. Marylebone and Notting Hill Infirmary, may be placed underneath the floor, and the grate occupy the centre of the room.

(53) Systems applicable for Schools and Public Buildings.

In the warming of schools and public buildings generally a combined system of warm air grates and of hot water or steam pipes is best. The air of school rooms and corridors may be warmed up to 50° by coils or radiators, and wherever more heat is required that additional degree may be obtained by open fireplaces.

Air that has been artificially heated, although heated in such a way that it is not contaminated by the gases of combustion, has nevertheless been changed and deteriorated in quality. Direct observation on the electric state of the air of close ill-ventilated rooms has shown that the electric condition of the air is reversed, and instead of being positive it is that which is called negative or resinous electricity. This change in the electrical state is probably accompanied by other changes such as a diminution of ozone, but direct observations on this point are wanting. The greater the degree the air is heated, the greater the change the air undergoes; hence any form of air heating in which the pipes are brought to a heat beyond boiling water, is to be deprecated.

(54) The High Pressure System.

In this system iron pipes of wrought iron are used, they are filled with water; at the highest point, there is a short bit of empty pipe called the "expansion pipe;" there is no boiler, the pipe passing direct through the furnace fire. In this closed system, there is necessarily great pressure, and the temperature and the pressure have a direct relationship. A modern and good improvement consists in the addition of a safety valve. The faults of the system

are the great irregularity in the temperature of different parts of the same coil, and the rapidity with which any slackening of the fire diminishes the heat. The danger from explosion is not great; if a pipe should burst it merely splits and there is a sudden rush of water and steam, but no fragments of metal fly about. Although from the defects mentioned and especially from the liability by the use of high pressure pipes to overheat the air, the writer considers the system objectionable for the purpose of warming houses; on the other hand it is useful for the purpose of heating drying closets and for disinfecting chambers; wherever in short a small space has to be brought to a high temperature.

(55) Steam Heating.

This is only suitable for buildings large enough to support the expense of constant and skilled supervision. The advantages of a steam apparatus over a hot water apparatus consist chiefly in the greater ease of application of the heating surfaces, where great inequalities of level occur, especially when the boiler has to be placed above the places to be heated as well as in the smaller heating surface required. The disadvantages are the constant skilled attention already mentioned, the want of permanence of temperature unless supervised with great care ; added to this, more fuel is required and the wear and tear is greater than in the case of a hot water apparatus.

(56) Hot Water Systems.

The ordinary hot water apparatus consists of a service cistern, a cistern at the highest point-a boiler and pipes extending from the boiler to the highest cistern and from the highest cistern back to the boiler; at any part of the course the pipes can be curled in coils or otherwise arranged to increase the heating surface. The water in the system is continually circulating, the hot water rising from its lower specific gravity in the one pipe and descending when cooled by its higher specific gravity in the other pipe.

The pipes can be usually maintained to 200°, a temperature that does not seem to deteriorate perceptibly the air passing over them.

It may be useful to know how to calculate the length of pipe