e any provision for the outlet of spent air, and if
ventilation is thought of at all, the only idea usually is to provide,
in part at least, for the admission of air and to make no adequate
arrangement for its egress. Whenever a stove or fire-place is in use,
the mere burning of fuel requires the consumption of air, and in cases
where apparently no air is admitted to the room, insensible ventilation
is at work bringing into the room, through the walls and through cracks
around the doors and windows, the necessary air for combustion.

[Illustration: FIG. 17.--Ventilation by means of coal stove.]

It may be proved by the laws of physics that a coal stove burning freely
in a room causes adequate ventilation; and that only where the dampers
of the stove are closed, so that not merely is the supply of fresh air
diminished, but also the products of combustion are thrown out into the
room, is there danger from lack of ventilation. The stovepipe in this
case furnishes the necessary outlet for the impure air, and the
following suggestion has been made in order to utilize this outlet, even
when the fire is not burning freely or when the damper in the stovepipe
is closed. If the stovepipe from a stove is carried horizontally, as it
usually is, an elbow must be provided to raise the pipe to the stove
hole in the chimney. Then providing a T connection at the point marked
_A_ in Fig. 17 (after Billings), the lower part of the _T_ may be
carried to within a foot of the floor with a damper at the points _B_
and _C_. When the fire is burning freely, the damper at _C_ is closed,
and ventilation is secured through the stove, the damper at _B_ being
open. When the damper at _B_ is closed and the fire checked, then the
damper at _C_ may be opened and the impure air drawn up the chimney from
the level of the floor. This, it is said, is an effective arrangement
for drawing off the polluted air of a room.

[Illustration: FIG. 18.--Coal-stove ventilation.]

Another method is to surround the stove with a sheet-iron casing, as
shown in Fig. 18 (after Billings), the top of the casing having a pipe
leading into the chimney independently from the stovepipe. The casing
becomes warm and heats the room by radiation, just as the stove does,
but if the damper in the flue from the casing be opened partly, a strong
draft along the floor and into this casing will be developed and the
foul air thereby discharged into the chimney. It will be easily
possibl