158. The heating and ventilation of buildings and the problems connected therewith are matters of serious concern to all who live in winter in the temperate zone. Not only should the air in living rooms be comfortably heated, but it should be continually changed especially in the crowded rooms of public buildings, as those of schools, churches, and assembly halls, so that each person may be supplied with 30 or more cubic feet of fresh air per minute. In the colonial days, the open fire place afforded the ordinary means for heating rooms. This heated the room mainly by radiation. It was wasteful as most of the heat passed up the chimney. This mode of heating secured ample ventilation. Fire places are sometimes built in modern homes as an aid to ventilation.
Benjamin Franklin seeing the waste of heat in the open fire places devised an iron box to contain the fire. This was placed in the room and provided heat by conduction, convection, and radiation. It was called Franklin's stove and in many forms is still commonly used. It saves a large part of the heat produced by burning the fuel and some ventilation is provided by its draft.
Fig. 141.—Heating and ventilating by means of a hot-air furnace.
159. Heating by Hot Air.—The presence of stoves in living rooms of homes is accompanied by the annoyance of scattered fuel, dust, ashes, smoke, etc. One attempt to remove this inconvenience led to placing a large stove or fire box in the basement or cellar, surrounding this with a jacket to provide a space for heating air which is then conducted by pipes to the rooms above. This device is called the hot-air furnace. (See Fig. 141.) The heated air rises because it is pushed up by colder, denser air which enters through the cold-air pipes. The hot-air furnace provides a good circulation of warm air and also ventilation, provided some cold air is admitted to the furnace from the outside. One objection to its use is that it may not heat a building evenly, one part being very hot while another may be cool. To provide even and sufficient heat throughout a large building, use is made of hot water or steam heating.
Fig. 142.—A hot-water system of heating.
Fig. 143.—One-pipe system of steam heating.