METHODS OF DOMESTIC HEATING
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 108 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 109 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° 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° Fahr., to empty the ewers and bottles that may be in the room. From 32° Fahr. to 40° Fahr. the room will be very cold, up to and including 58° Fahr. it will be too cold to be pleasant; the standard temperature may be taken as between 62° and 64° 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, 110 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.