In weather when artificial heat is necessary for comfort, thorough ventilation is not difficult, provided expense is not considered. As the removal of the foul air, however, involves a considerable waste of heat and consumption of fuel, the means of procuring the best ventilation at the least cost becomes a problem of great intricacy, which has not yet been satisfactorily solved. =Fireplaces=, or open grates, are excellent ventilators. An ordinary fireplace renews the air of the room four or five times hourly, removing in that time from fifteen to twenty thousand cubic feet of air. But only about 12 or 14 per cent. of the heat given off by the fuel is utilized, the rest passing off by the chimney. The objections to the fireplace as a sole means of heating are, its wastefulness, and the fact that it warms only by radiation, so that the room is unequally warmed, and may be too cold in one place and insupportably hot in another. =Stoves= and =furnaces= can not be relied on for ventilation, the ventilating power of a close stove being only one tenth of that required for a single adult. Modern fireplaces are sometimes built with a metallic flue extending upward into the chimney. Between this flue and the masonry is an air-chamber opening to the external air and communicating with the room near the ceiling, so that fresh air from outside the house is continuously warmed, and discharged into the room at a temperature of 80° or 90°. The Galton fireplace (Fig. 1) is of this kind, and utilizes 35 per cent. of the fuel. The best combined heating and ventilating arrangement at present seems to be that which warms the fresh air by means of a soapstone furnace or steam-coils, and removes the foul air through a fireplace. In milder weather, gas may be burned in the chimney at a slight expense. According to Morin, seven cubic feet of gas burned in a flue eleven inches square and sixty-six feet high, will draw thirteen thousand three hundred cubic feet of air per hour from a room. [Illustration: Fig. 1.—Galton’s fireplace.] The =dampers= of stoves should never be in the pipes, for they dam back the gases which ought to enter the chimney, and force them into the room. The fire should be regulated by dampers which prevent the access of air, and not its escape after contamination. Ventilating =flues= in walls do very little good, unless special means are provided to heat them (e. g., gas lights or lamps). The common whirling ventilators in window-panes are of very little use. As a rule, fresh air should enter a room near the ceiling, and foul air be removed near the floor. In very cold climates, dangerous draughts are often produced by the cooling of the air in contact with the window-panes, so that it falls and sweeps along the floor. This danger may be prevented by double windows, which also save fuel. Double windows may be utilized in ventilation, by raising the lower outer sash a few inches, and lowering the upper inner one.