220 WATER, HEAT, AIR, AND LIGHT IN THE HOUSE 



wind is blowing strongly, the openings should be on the side opposite 

 the wind. 



When a large room is heated by a stove, the stove should be sur- 

 rounded by a "drum," open-at the top and bottom, and reaching from 

 near the floor to a point some distance above the stove-top. The 

 drum should be in two parts, hinged together, so that the stove may be 

 easily reached. The circulation of air in the room is then not left to 

 chance; for the drum not only protects those nearest the stove from 

 excessive heat, but it also sets up useful convection currents. These 

 bring cold air from the farthest parts of the room to the stove, heat it, 

 and then carry it away along the ceiling. The room is thus heated 

 evenly, and ventilated at the same time. 



Heating Systems and Ventilation. The hot-air furnace brings in 

 fresh, warm air; but the removal of the cooled, foul air is left to the 

 cracks of the room. The fireplace, since its opening is near the floor, 

 is an excellent aid to the hot-air furnace. Stoves provide some ven- 

 tilation; since fresh air from outside must come in to take the place of 

 the air that goes through the stove. Hot water and steam heating 

 systems of themselves give no ventilation. 



249. Need of Moisture in Air. One very important 

 constituent of fresh air must not be forgotten : its mois- 

 ture. We find air very comfortable, at any given tempera- 

 ture, if it has between 2 /5 and 2 /s of the water it can hold 

 at that temperature. Such air takes up the perspiration 

 at a moderate rate, and so regulates the heat of the body. 

 But if the moisture is more than 2 /s of what the air can 

 hold, we are uncomfortable; the perspiration does not 

 evaporate rapidly enough, and the air feels " sticky. " 

 When too little moisture is present, the perspiration evapo- 

 rates too rapidly. The skin then becomes parched and dry. 



As a result of artificial heating and ventilation the 

 amount of air moisture in a house is almost sure to be too 

 small. The reason for this is that the cold air entering a 



