HEATING and VENTILATION. In cold climates, artificial heating and ven tilation are both necessary for health and comfort and are equally important. Because the discomfort produced by low temperature is more acutely and im mediately felt than that due to foul air, improper ventilation is more common than deficient heating. The two subjects are so closely related, however, that they will be considered together in this article, the question of heating being first dealt with in greater detail.
The temperature most conducive to bodily comfort cannot be stated definite ly as it is largely determined by climate and personal habit, varying in different countries. A temperature of 68-70° F. is considered necessary in the U. S. A. and Canada, but 62° F. is the tempera ture most favored in England. All sys tems of heating depend upon radiation or convection; or, more generally, upon a combination of the two. The common est example of radiation is the open fireplace which radiates heat, and so warms the walls and furniture of the room, while leaving the air compar atively cool. An example of convection is found in the hot air furnace, which supplies currents of warm air, which constantly replace the cold air. Radia tion and convection combined are found in the ordinary steam or hot water radi ator, which heats the air by convection and also radiates some heat to sur rounding objects. Heat is most com monly produced by the combustion of coal, wood, coke, oil, gas, or some other fuel, but is occasionally obtained elec trically, the electricity being produced by water-power.
Comparing the relative merits of the different forms of heating the open fire place is popular because it is cheerful to see, and from the hygienic point of view it is good because it produces a simple but efficient means of ventilation. It utilizes, however, only 10-15 per cent.
of the heating value of the fuel, and, unless supplemented by other forms of heating, is quite inadequate for pro viding sufficient heat in cold climates. The stove which stands out in the room, being connected to the chimney by a pipe, is upward of 50 per cent. efficient, but it has the disadvantage of being dusty, and of quickly producing foul dry air unless careful attention is given to ventilation. The hot-air furnace is of two types. The older type conveys the heated air from a central chamber to various parts of the house by means of pipes; the more modern type is pipeless, the heat entering the upper part of the house from a single register on the first floor, and being carried by convection to all parts of the house. The furnace is supplied with fresh air from the out side, and provided this feature is prop• erly cared for, a hot air system is prob ably the most healthful method of heat ing a dwelling. With the old type of furnace, however, it is difficult to obtain uniform heating, the rooms on the wind ward side of the house being cold, while those on the sheltered side are over heated. The pipeless furnace is growing
in popularity, and gives satisfaction in houses of suitable size and design. The steam furnace generates steam from a boiler in the cellar and distributes it over the house by means of pipes con nected to radiators. The hot-water fur nace is similar, except that hot water instead of steam circulates through the pipes and radiators. Both systems have advantages and disadvantages. Hot wa ter is more difficult and expensive to install but has the advantage that it begins to supply warmth as soon as the water becomes heated, whereas, with steam, the water must boil before heat is supplied. Hot water is also quieter than steam, but high temperatures can be produced more rapidly with the latter and much less radiating surface is needed. A modern development of steam heat is the so-called "vacuum system," in which the whole system of piping and radiators is maintained under a slight vacuum. One advantage of this system is that the knocking and hissing of the radiators is avoided. Another recent modification is the gas-steam radiator, which is a radiator having a small res ervoir of water at the base, heated by gas burners. As the pressure, due to gen eration of steam, rises, the gas is auto matically lowered. Electric heating is too expensive for use on a large scale, but finds application in small heaters for intermittent use, and also in the heating of street cars.
steady supply of fresh air is necessary to the well-being of the animal body, because one-fifth of the air consists of oxygen and it is upon oxygen that the heat and energy of the body depends. When fuel burns, carbonic acid gas is produced. The same gas is con tained in the breath from the body, and to produce this carbonic acid, oxy gen is absorbed from the surrounding air. An excess of carbonic acid in the air produces headache, depression and even nausea, and anything in excess of six parts per ten thousand is liable to cause discomfort. A gas burner, in a small room, will very quickly pollute the air, and for every cubic foot of gas con sumed, eight cubic feet of air are ex hausted of their oxygen. It is estimated that one person requires 3,000 cubic feet of air per hour. That is to say, a room 30 feet long, 10 feet high and 10 feet wide contains sufficient air to supply one per son for one hour, but it is clear that no one could live in a hermetically sealed room of such a size for that length of time without suffering from poisoning, because throughout the time he would be polluting the air and the pollution would pass the safe limit very soon. In the ordinary room, of course, there is constant leakage of bad air and ad mittance of pure air through cracks and in the doors and windows, through the chimney and by other accidental means. In actual practice, it is found that 250 300 cubic feet per person in dwellings and factories is sufficient.