Ventilation and Heating. 1 1 7 



there is a grate in a room, it serves very well as a foul-air 

 shaft, especially when there is a fire in the grate. It is 

 well to have the flue from the grate in the same chimney 

 with that from the smoke-pipe from the furnace, as then the 

 heat from the smoke will cause a constant up-draft in the 

 grate flue, whether there is a fire going in the grate or not. 



With a grate, in private houses, there is ordinarily no 

 need of other foul-air shaft for any room. But it is very 

 desirable to have at least some " indirect " heat, so that 

 the fresh air introduced will be sufficiently heated. 



If the introduction of air is thus provided for, it is then 

 safe to put on double windows and make the cracks around 

 the door very tight. Without any special provision for the 

 renewal of the air these cracks are the means of safety. In 

 houses heated by furnaces, steam, or hot water, the floor 

 is likely to be warmer from the escape of heat from the 

 heater itself, and from pipes or air ducts under the floor. 



Double Windows. There is a very common misunder- 

 standing as to the cold felt near a window in cold weather. 

 It seems that air is entering; but a little reflection will 

 show that even if the window were air-tight this effect 

 would be produced, for the air near the window is cooled 

 by losing heat to the outer air through the glass. The air 

 next to the window, thus cooled, is heavier, and falls to the 

 floor ; and if there is any source of heat in the room, this 

 cold air will pass along the floor to that source of heat, up 

 from the heating body to the ceiling, and across the ceil- 

 ing, and so on around again. There may thus be currents 

 without any change in the quality of the air. It is 

 economy to use double windows and prevent the loss of 

 heat through the glass. So both economy and comfort 

 suggest to us that we reduce as much as possible cracks 

 around doors and windows, use double windows, make 



