The two methods of warming a house are by radiation and conduction. We
may surmise that in any case both methods will be in use, but the one
will predominate; for instance, in heating by an open fire radiation
will predominate, and in heating by stoves and radiators conduction will
predominate. In planning a house a decision must be made between the
two. This decision being made there is the further consideration of
where the source of heat shall be placed. In the case of an open
fireplace shall it be in an end wall, in a corner, in an outside wall,
and so on, the object being to make the greatest possible use of the
heat that passes up the chimney and of that which radiates into the
room. The same consideration must be paid to the situation of the closed
stove; where will it pass heat by conduction to the greatest volume of
air, and where can its radiant heat be utilised?
In a room heated by a stove there is frequently a vessel of water placed
by or on the top of the stove. If we ask what is the purpose of this
water we shall be told that the stove dries the air in the room. Now, it
is impossible that the heat of the stove should remove any moisture from
the air; we must therefore seek an answer to the question, What is dry
air? The sensation of the dryness or moisture of the air does not depend
only upon the amount of vapour in the air but upon the ratio of the
amount present to the amount that the air is able to hold at the given
temperature. The warmer the air is the more vapour it can hold, hence
when the air is warmed the percentage of water present to the possible
amount in it is lowered; that is its humidity, which is the percentage
amount, is lowered, and we feel it to be dry. The question may arise why
we should feel this when the room is heated by a stove and not when it
is heated by an open fire? It may be that in a room with an open fire we
are warmed by radiation and give out heat to the surrounding air which
is constantly changed by convection currents, so that the air we breathe
is colder than we ourselves; and that in a room warmed by a stove we
receive heat from the air and are constantly breathing air that is
warmer than we ourselves. But it is more than probable that the custom
of providing a source of moisture to the air persists from the
suggestion of a single person in seeking to relieve the disagreeable
feeling attending the breathing of air laden with the poisonous products
of half-consumed gas, and that it has no real scientific foundation.
_How to estimate temperatures._--Whatever method is adopted for warming
a room, the housewife may be assured that the resulting temperature will
not be pleasing to every member of the family. One will find it too
warm, and another will at the same time find it too cold, and this not
from any wilful captiousness but from the cause that we have already
alluded to, that the feelings are a very uncertain test of temperature.
It is therefore advisable to keep the air of the room as far as possible
at a standard temperature. To do this it will be necessary to have a
thermometer in the room, and to know what its readings indicate. When
the thermometer registers 32 deg. Fahr. or less, water will freeze in the
room, and the vessels in which it is kept will burst; it is therefore
wise, when it is anticipated that the temperature will fall below 32 deg.
Fahr., to empty the ewers and bottles that may be in the room. From 32 deg.
Fahr. to 40 deg. Fahr. the room will be very cold, up to and including 58 deg.
Fahr. it will be too cold to be pleasant; the standard temperature may
be taken as between 62 deg. and 64 deg. Fahr.
It may appear a simple matter to hang up a thermometer and read it, but
a little thought will show that it is not so easy as it seems. If, for
instance, the thermometer is placed in front of the fire at a distance,
say of four feet from it, what will its reading indicate? Will it be the
temperature of the air of the room or the temperature of the fire, or if
neither, what will it be? Suppose we have two identical thermometers,
and hang them on adjacent walls, one of which is an outside wall, which
of the two readings shall we take as that of the temperature of the
room? It is not an easy matter to decide. In a sick-room, where one
person's comfort only has to be considered the doctor will order the
thermometer to be hung at the bed-head, but we cannot adopt this plan in
a general sitting-room.