e, of course, to carry away all the heat from the stove in this
method, and the damper in the flue of the casing must be carefully
regulated to carry away only the desired amount of foul air.

[Illustration: FIG. 19.--Coal-stove ventilation.]

Still another method of using the heat of a stove to secure ventilation
is shown in Fig. 19 (after Billings). Here the stove is surrounded with
a sheet-iron jacket extending from the floor to about six feet above
that level. A pipe is carried from the outside air up through the floor
directly under the stove. By regulating the damper in this pipe the
supply of fresh warmed air entering the room can be regulated. Doors in
the casing must, of course, be provided for the purpose of taking care
of the fire, and of allowing air from the room near the floor to be
heated instead of the outside air.

A most objectionable method of providing an outlet for polluted air from
a room is to have a register in the ceiling with the ostensible purpose
of warming the room above. It was the writer's misfortune once to stay a
week in the country, in a room over the kitchen where this method of
heating was employed, and the odors of cabbage, onions, and codfish
which permeated the upper room, and clung there all night, still remain
as a most unpleasant memory.

_Size of openings for fresh air._

As an indication of the size of the openings needed, it has been said
that in order to provide the necessary air movement, and yet to restrict
the velocity of the moving air so that no objectionable drafts will be
experienced, at least twenty-four square inches sectional area should be
allowed as an inlet for each person, so that one square foot is required
for six persons. This is, perhaps, a theoretical requirement. Certainly,
it is more area than is likely to be obtained in actual ventilation. The
space between two windows, for instance, is about one inch by thirty
inches,--barely enough, according to this rule, for one person, and yet
that opening is sufficient to appreciably improve the quality of the air
in a room occupied by three or four persons.

Taking into account the necessary air required by lamps or gas burners,
the inlet flue should have at least ten square inches area for each
person, so that the ordinary single register should provide the
necessary amount of air for a living room. When, as happens in houses
where a studied effort is made to preserve the health of the
inhabitants, an outl