[14] These outlets may be placed close to a chimney or heating pipes. Warm air rises and thus will be forced out, allowing cool fresh air to enter at the inlets.--EDITOR. [15] The ordinary dwelling house needs no artificial methods of ventilation. The opening and closing of windows will supply all necessary regulation in this regard. The temperature of living rooms should be kept, in general, at 70 deg. F. Almost all rooms for the sick are unfortunately overheated. Cool, fresh air is one of the most potent means of curing disease. Overheated rooms are a menace to health.--EDITOR. CHAPTER III =Warming= =Ventilation and Heating.=--The subject of the heating of our rooms and houses is very closely allied to that of ventilation, not only because both are a special necessity at the same time of the year, but also because we cannot heat a room without at the same time having to ventilate it by providing an egress for the products of combustion and introducing fresh air to replace the vitiated. =Need of Heating.=--In a large part of the country, and during the greater period of the year, some mode of artificial heating of rooms is absolutely necessary for our comfort and health. The temperature of the body is 98 deg. to 99 deg. F., and there is a constant radiation of heat due to the cooling of the body surface. If the external temperature is very much below that of the body, and if the low temperature is prolonged, the radiation of heat from the body is too rapid, and colds, pneumonia, etc., result. The temperature essential for the individual varies according to age, constitution, health, environment, occupation, etc. A child, a sick person, or one at rest requires a relatively higher temperature than a healthy adult at work. The mean temperature of a room most conducive to the health of the average person is from 65 deg. to 75 deg. F. =The Three Methods of Heating.=--The heating of a room can be accomplished either _directly_ by the rays of the sun or processes of combustion. We thus receive _radiant_ heat, exemplified by that of open fires and grates. Or, the heating of places can be accomplished by the heat of combustion being conducted through certain materials, like brick walls, tile, stone, and also iron; this is _conductive_ heat, as afforded by stoves, etc. Or, the heat is _conveyed_ by means of air, water, or steam from one place to another, as in the hot-water, hot-air, and steam systems of heating; this we call _convected_ heat. There is no strict line of demarcation differentiating the three methods of heating, as it is possible that a radiant heat may at the same time be conductive as well as convective--as is the case in the Galton fireplace, etc.