Ventilation does not necessarily mean draughts of cold air, as is too often supposed. In warming by indirect radiation it may readily be secured by fixing, in addition to the registers from which the fresh warmed air reaches the room, corresponding openings at the opposite side by which the old air may pass off to make room for the new. An open fire in a room will always keep up a current of air through it, and is one of the most wholesome, though not most economical, methods of warming an apartment.

Why are the injurious effects of impure air apt to be ignored?

What volume of air should be allowed to each adult? At what rate should it be replenished? What supply of fresh air is needed to keep an inhabited room free from odor? Is it safe to live in a room which " smells close"?

How may ventilation be secured in heating by " indirect radiation"? What are the advantages and what the disadvantages of an open fire?

Stoves in a room unless constantly supplied with fresh air from without dry its air to an unwholesome extent. If no appliance for providing this supply exists in a room it can usually be got, without a draught, by fixing a board about four inches wide under the lower sash and shutting the window down on it. Fresh air then comes in by the opening between the two sashes and in a current directed upwards, which gradually diffuses itself over the room without being felt as a draught at any one point. In the method of heating by direct radiation the apparatus employed provides of itself no means of drawing fresh air into a room, as the draught up the chimney of an open fireplace or of a stove does; and therefore special inlet and outlet openings are very necessary. Since, fortunately, few doors and windows fit quite tight, fresh air gets into closed rooms in tolerable abundance for one or two inhabitants.