Management of a furnace.

Many hot-air furnaces have a "hot-water attachment," or combination," consisting of a cast-iron receptacle, of form varying according to the furnace used, or, sometimes, of a coil of pipe, suspended in the drum of the furnace, which is kept full of water, and connects, by flow and return pipes, with hot-water radiators in certain rooms. These attachments are valuable for carrying heat to rooms which cannot well be supplied with hot air from the furnace, and require little care, except to keep the radiators from freezing, and not to build a fire in the furnace unless the water attachment is full of water, for fear of burning it out. They add to the quantity of coal consumed, particularly if the pipes leading to the radiators are exposed to cold air; and it is well to remember that where the hot-water heater is placed at the very top of the drum, as is sometimes the case, the coal should be piled well up, so as to get the fire as near as possible to the water, in order to secure satisfactory results. If well managed, such hot-water attachments make it practicable to heat with the furnace rooms so far away from it that hot air could not be made to flow into them, or so situated that a tin hot-air pipe could not be carried to them without disfiguring some other room.

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Hot-water attachments.

The tin pipes used for conveying the hot air from the air-chamber of a furnace to the rooms to be heated, and the registers through which it is delivered, are important portions of the heating system. Much heat is lost during the passage of the air through the pipes, particularly if these are long, or pass through cold rooms, or near outside doors; and they should, in these places, as well as where they are carried up in partitions, either be made double, consisting of two pipes, with a quarter-inch or half-inch airspace between them, or wrapped with non-conducting and non-inflammable asbestos paper; or the two systems may be united, making the pipes double, as well as covering them with asbestos, where the best results are desired. Where two pipes run side by side, it is advantageous to unite them in the same wrapping of asbestos, so that one may warm the other. With all the care that can be taken, it rarely happens that all the rooms in a furnace-heated house can be warmed equally under all conditions of wind. The force which sends hot air through a pipe, being, usually, simply the difference in weight between the warm air in the pipe and an equal bulk of cold air, is so slight that a very small circumstance may affect it; and, in a high wind, the natural tendency of the air in the house toward the lee side usually carries with it the warm currents through the registers, which flow freely into the rooms on the side of the house away from the wind, but can hardly be felt in the rooms on the windward side. In order to counteract, to a certain extent, this effect, it is usual to direct the opening of the cold-air box, by which fresh air is taken from the outside to supply the air-chamber of the furnace, toward the north or west, so that the coldest winds may blow into it, and increase in that way the force of the current through all the registers; and a furnace is occasionally seen fitted with two fresh-air inlets, one on the east side of the house, and the other on the north or west side, so that advantage may be taken, by closing the inlet on the lee side, and opening that on the windward side, of any cold wind.

Hot-air pipes and registers.

With a reasonably efficient furnace, there is little danger that all the air which will blow in through an ordinary cold-air box cannot be heated after the fire is properly started. Until then, as the circulation of a strong current of cold air through the air-chamber chills and checks a feeble fire, it is often advisable to shut off a part of the air-supply. The full supply should, however, be restored as soon as the fire has gained strength enough to be capable of warming it. If this is not done, either air will be drawn from the cellar, through crevices in the cold-air box, or some of the registers will be deprived of heat, as very few cold-air boxes are designed of sufficient size to supply all the registers dependent upon them without the aid of the wind blowing into them, or of air from the cellar. The proper sectional area of the cold-air box is the sum of the sectional areas of all the hot-air pipes, less one-sixth, this fraction representing the expansion of the cold air by heating. Where the capacity of the cold-air box is less than this, the air must be economized, at least in calm weather, by shutting off a part of the supply to some of the registers, by partially closing the dampers in the pipes which convey warm air to them. If this is not done, the registers most favorably situated will draw air down through those less so, to make up for the deficiency of fresh air from the outside. The dampers for this purpose, as well as for equalizing the distribution among the various rooms, are, or should be, placed in the hot-air pipes, near the furnace; and, where the heat is to be entirely shut off from rooms which are not occupied, the same dampers should be used for the purpose, so that heat may not be wasted in the pipes leading to the unoccupied rooms.

Air-supply.

Of the troubles to which furnace-heated houses are subject, the most common is the unequal heating of the rooms. To a certain extent this is inevitable, a perfectly uniform distribution of the warm air being impracticable; but much may be done to equalize the currents, or, at least, the heat of the rooms which they supply. In general, the higher a pipe ascends, the stronger will be the current through it, for the reason that the difference of weight between the column of warm air in it, and a column of equal height of the exterior air, is correspondingly greater. This is the reason why furnace-pipes to upper rooms are always made smaller than those to first-story rooms, the rapidity of the flow of air through them making up for its diminished volume; and advantage can often be taken of this principle to increase materially the delivery of warm air into a room with a register in the floor by setting up over the register a pasteboard cylinder, or rectangular box, according to the shape of the register, open at both ends, and four or five feet high. This simple device, when used in first-story rooms, may more than double the height of the warm column, and, under some circumstances, greatly improve the heating of the room.