Mechanics of the Household. E. S. Keene
Fig. 43a.—Details of construction of the hot-water radiator valve.
Hot-water Radiator Valves.
—Valves for hot-water radiators differ materially from those used on steam radiators. Figs. 43 and 43a show the outside appearance and the mechanical arrangement of the parts of the Ohio hot-water valve. The part A in Fig. 43a is a hollow brass cylinder attached to the valve-stem, one side of which has been removed. When it is desired to shut off the supply of heat the handle of the valve is given one-quarter turn and the part A covers the opening to the inlet pipe. The supply of water being shut off, the radiator gradually cools. When the valve is closed a small amount of water is admitted to the radiator through a 1⁄8-inch hole in the piece A to prevent the possibility of freezing.
Air Vents.
—In the use of the systems of hot-water heating described, every radiator must be supplied with an air vent of some kind to take away the trapped air which accumulates through use. Any kind of a valve will serve as a vent for hand regulation and generally such a cock as is shown in Fig. 10 is employed.
Fig. 44.—Automatic air vent for hot-water radiators.
Automatic Hot-water Air Vents.
—It is sometimes desired to use automatic air vents on hot-water radiators. For such work a vent is used that remains closed as long as water is present and will open when the water is displaced by the accumulating air, but will again close when the air is discharged. In such vents the valve is controlled by a float, the buoyancy of the float when surrounded by water serving to keep the valve closed. These vents are not so positive in their action as automatic air vents for steam. The change in temperature which controls the steam vent does not take place with hot water. The automatic hot-water vents are not perfectly reliable. They may work with entire satisfaction for a long time and then fail from very slight cause. The failure of a hot-water vent is generally discovered by finding a pool of water on the floor or a wet spot on the ceiling or wall of the floor below.
One type of the automatic hot-water vent that has proven quite successful is shown in Fig. 44. The threaded lug is screwed into the radiator at the proper point. As the water enters the radiator the air is discharged through the vent, escaping at the opening C. When the water has risen to a sufficient height it enters the openings G and H until enough is present to raise the float A. The pointed stem attached closed the hole C with sufficient force to make an air-tight joint. The float A is a very light copper cylinder. Its buoyancy supplies the force to close the vent and its weight opens the vent when the water is displaced by air. It will be readily seen that very slight cause might prevent the performance of its duty.
CHAPTER III
THE HOT-AIR FURNACE
Of the methods of heating dwellings other than by stoves, that of the hot-air furnace is the most common. Of the various modes of furnace heating it is the least expensive in first cost and most rapid in effect. In the use of steam heat, the water in the boiler must be vaporized before its heat is available. With hot-water heating, the whole mass of water in the entire system must be raised considerably in temperature before its heat can affect the temperature of the rooms, and consequently in first effect it is very slow. In the use of the hot-air furnace the heat from the register begins to warm the rooms when the fire is started.
Hot-air furnaces are made by manufacturing companies in a great variety of styles and forms to suit purposes of every kind. In practice the furnace is built in sizes, to heat a definite amount of cubical space. The maker designs a furnace to heat a certain number of cubic feet of space contained in a building. It must be sufficiently large to keep the temperature at 70°F. on the coldest nights of winter when the wind is blowing a gale. It is evident that with the variable factors entering the problem, the designer must be a person of experience in order that the furnace meet the requirements.
The following table taken from a manufacturer’s catalogue shows the method of adapting the product of the maker to any size of dwelling. The volume of the house is calculated in cubic feet and from this result the size of furnace most nearly suited is selected from the table.
| Furnace number | 1 | 2 | 3 | 4 | 5 |
| Weight without casing, lb. | 984 | 1,111 | 1,340 | 1,531 | 1,934 |
| Estimated capacities in cubic feet | 8,000 to 12,000 | 12,000 to 20,000 | 20,000 to 35,000 | 35,000 to 60,000 | 60,000 to 100,000 |
| Capacity in number of rooms of ordinary size in residence heating | 3 to 5 | 5 to 7 | 7 to 9 | 9 to 12 | 12 to 15 |
CONSTRUCTION
Fig. 45.—Interior view of a hot-air furnace.
The furnace, in general construction, consists of a cast-iron fire-box with its heating surfaces, through which the flames and heated gases from the fire pass, on the way to the chimney; these with the passages and heating surfaces for heating the air compose the essential features. Fig. 45 shows such a furnace with the sides broken away to show the internal construction. The flames and gases from the fire-box F circulate through the cast-iron drum D and are discharged at C to the chimney. The drum D is made in such form that it presents to the heat from the fire a large amount of heating surface and at the same time offers as little opposition as possible to the furnace draft. The air to be heated enters the furnace through the cold air duct at the bottom, and after circulating through the drum, passes out at the openings R to the conducting pipes. The cast-iron box W is a water tank that should be attached to every hot-air furnace. The water contained in the tank is for humidifying the air as it passes through the furnace. In this furnace the outside casing is of sheet iron, reinforced with wrought-iron flanges. The front, which contains the doors of the fire-box, ash-pit, etc., are of cast iron of ornamented design.
As the air to be heated passes through the furnace it receives part of its warmth by radiation but most of it is absorbed by coming directly into contact with the heating surfaces. Since air is a poor conductor of heat its temperature is raised very slowly; it should, therefore, be kept in contact with the heating surfaces as long as possible to insure an economical furnace. In common practice the ratio of heating surface to grate surface average 35 to 1; that is, for each square foot of grate surface there is 35 square feet of heating surface to warm the passing air. Should this ratio be increased to 50 to 1 the efficiency of the furnace would be much improved.
If the ratio of heating surface to