The most recent improvements in the use of the German stove for warming have been introduced by Dr. Bohm, in the Rudolf Hospital at Vienna. He there warms fresh air by means of passages constructed in the fire-clay stoves, placed in the ward, and the fresh warmed air passes into the ward from the top of the stove. He provides flues of a large size, and proportioned to the size of the ward, from the level of the ward floor to above the roof, and the difference of temperature between the air in the ward and the outer air causes a sufficient current in these flues to ventilate adequately the ward. By this means the fresh warmed air, instead of passing off to the upper part of the ward and then away by flues there, is made to circulate toward the floor of the ward, thus bringing into action the principle by which the open fireplace is useful in ventilation. But this arrangement destroys one element of economy in the German stove, because the heat generated, instead of being left to pass slowly off into an unventilated room, is removed rapidly by the fresh air passed into the ward, and has, therefore, to be renewed at intervals, instead of, according to usual custom, the stove being left shut irp for twenty-four hours to give off its heat slowly. The larger the supply of warmed air, the larger must be the consumption of fuel; and, if the heat is to be supplied economically, it must be through a good conducting medium; but the material of the German stove is a bad conductor of heat.
The old Roman system of warming by means of a fire under the floor produced a most agreeable and equable temperature, but it did not assist the ventilation, and' it was not economical, in that the floor, being of tiles, was of a bad conducting material, and much of the heat was absorbed in the ground or surrounding flues. According to Pliny, the smoke was carried to the wood-house to be used in drying the wood for burning. I recently made an experiment to compare the effect of warming by means of a heated floor with the heating effect of a ventilating fireplace; the experiment lasted, with each mode of warming, for two days. It showed that, in the case of the warmed floors, the room was maintained at a temperature of about 18° above the temperature of the outer air with an expenditure of 56 lbs. of coal and 112 lbs. of coke, while with the ventilating fireplace the expenditure was only 75 lbs. of coal; the cost being 3s. 4d. for the warmed floor as compared with 1s. 4d. for the ventilating fireplace.
A more complete plan of warming a building is by means of a fire from which the heat is conveyed, either by hot-water pipes or hot air, to the various parts of the building.
Warming by means of air conveyed by flues to various parts of the building, will answer, as a rule, in ordinary existing houses, best in connection with open fireplaces, which draw in the warmed air to the various rooms, because there must be some means of forcing or drawing the warmed air into the house, and it would not be convenient to
