The Heater.-When hot-water heating was first introduced, tubular boilers, similar to steam boilers, only entirely filled with tubes, were used for heating the water. Within the past ten years, however, a great many special heaters have been patented that are intended especially for residences, such as the " Gurney,' Mer," "Gorton," and the "Furman." The American Boiler Company manufacture several, viz., the "Bolton,' ""Spence," "Tropic," Perfect," and Advance."

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Nearly all of these heaters are made up of a number of cast-iron sections, which are bolted together and the joints packed to make them water-tight. The flow pipes are taken from the top of the upper section, and the return pipes are connected with the lowest section, which generally forms either the fire-pot or the ash-pit.

The successful working of a hot-water heating apparatus depends very largely upon the proper construction of the boiler. It is generally admitted that in an efficient hot-water heater the water must be cut up into small portions, so as to heat quickly, and the whole arrangement of the heater should be such that the least possible resistance is offered to free circulation.

The boiler in which the most powerful circulation is maintained with the least consumption of fuel is the most satisfactory as well as the cheapest.

The method employed in connecting the joints, and the facilities for cleaning fire surfaces, are also points that should be carefully examined.

For the efficiency of the various sizes and styles of heaters, the architect or owner must, as in the case of hot-air furnaces, depend largely upon the tables given by the manufacturers.

As there is no pressure on the heater other than the weight of the water, no steam-gauges, safety-valves, or similar appliances are required, as is the case with steam.

Radiation. As has already been stated, the radiators and piping are practically the same for hot-water as for steam heat, except that, to heat a given space by hot-water circulation, more radiating surface is required than with steam.

The following ratio of heating surface to space heated is given by the Gurney Company, due allowance to be made for exposure, locality, glass surface, construction, and other conditions: Dwellings: One square foot of direct radiating surface will heat in parlor, sitting-room, living room, library, dining-room-from twenty-five to thirty-five cubic feet of air; hall, bath-room-from twenty to thirty cubic feet of air; sleeping rooms-from thirty to fifty cubic feet of air. For indirect radiation not less than fifty per

cent. more surface should be allowed, and for direct-indirect, twenty-five per cent. more.

Indirect Radiation.-Every residence heated, either by hotwater or steam radiation, should have at least two indirect radiators, to provide for some ventilation. These should be placed in the cellar, and connected with registers in the front hall and principal living room. The common method of providing for indirect radiation is explained on page 796:

Direct radiation, as has been explained elsewhere, simply heats the air in the room over and over, and not only does not afford any ventilation, but tends to decrease the vitalizing qualities of the air.

Expansion Tank.-Every job of hot-water heating (at least in residences) should have an open expansion tank, connected with the highest part of the flow-pipe. It should be placed in the bathroom or other convenient place, and not less than three feet above the highest radiator. The tank should be provided with a water-glass, to indicate the proper water level, which is usually about half-way up the glass. A one inch overflow pipe must also be provided, connected with tank about three or four inches from the top, and running to basement or other convenient place, where it will do no harm should the water in the expansion tark boil or overflow at any time. The expansion tank on a hot-water apparatus serves as a safety-valve. Should the water at any time be heated above the boiling-point, the steam finds its way through the flow-pipes to the tank, and thence escapes to the atmosphere. The expansion tank also allows the water in the system to expand or contract under. different temperatures without any injury to the apparatus. The capacity of the expansion tank should be at least one-twentieth of the whole capacity of the apparatus.

A hot-water apparatus is generally filled by connecting the house supply to return pipe at or near the heater. Sometimes a supply is connected with the expansion tank, and a ball-cock placed on it, to insure that there shall always be three or four inches of water in the tank. At the lowest point of apparatus a draw-off, or emptyingcock, should be placed, to empty the system at any time.

The apparatus should be kept full of water during the summer months. This excludes the air, and prevents corrosion or oxidation of pipes.

Hot-water heating requires a much more perfect apparatus than steam heating, and great care must be exercised in running and proportioning the flow and return pipes.

The following Advice to Fitters, published by the Gurney Heate

Manufacturing Company, contains many practical suggestions, that should be of almost equal interest to the architect and owner:

When estimating upon a job, take well into consideration the extent of all flow, return pipes, and risers, also their situation, and calculate them as radiating surface in addition to what is placed in rooms, and allow heater power accordingly.

Due care must be exercised to provide for any special conditions, such as exposure of building, material of construction, location, length and size of mains governing plant under consideration.

"Allowances should also be made for loose construction of doors and windows, which admit large volumes of cold air, and provide for outside doors which are used frequently, and open directly into the room..

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In estimating the radiating surface, it should be borne in mind that a large surface at a comparatively low temperature gives a much pleasanter atmosphere than a small surface at a high temperature.

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Excess of surface is no discomfort, as is the case with steam, since the temperature can easily be controlled by varying the fire, or by valve on radiator.

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'All flow and return pipes in cellar should be properly covered with hair-felt or some other good non-conducting material, to obtain the best and most economical results. Doing this will save one-sixth of the heat. If no covering is used, paint heater and pipe exposed in basement a black or maroon japan; neat and attractive piping goes far toward securing other contracts.”

For a thorough and comprehensive treatise on hot-water heating and fitting, the reader is referred to a work on this subject by Mr. William J. Baldwin, published by the Engineering Record. Much valuable information may be found in the catalogues of the Gurney Heater Manufacturing Company, the H. B. Smith Company, and others.

Specification.

The following form may serve as a guide in specifying hot-water heating for residences :

SPECIFICATION FOR HOT-WATER HEATING APPARATUS, IN RESIDENCE FOR JOHN JONES, ESQ., BROOKLINE, MASS.

Heater.-Furnish and set up in cellar one No. (120 GURNEY) HOT-WATER HEATER, having fire, ash, and cleaning-out doors, shaking and sliding grate, with handle, draught dampers, and set of fire tools.

Make iron smoke connections to chimney; a flue of sufficient size to be furnished by the owner.

Trimmings.-Furnish all necessary trimmings, such as direct feed-cock, drawoff cock, for the purpose of filling and emptying the apparatus at any time. The owner will furnish foundation to set heater upon in cellar, of proper size of base.

Pipes.-Furnish and run all necessary flow and return pipes of ample size, connecting them to radiators with one-inch pipe (for each radiator) up to 52 square feet of surface, and one and a quarter inch to radiators over 52 square feet surface, and up to 120 square feet; over 120 square feet surface, one and onehalf inch connections; said pipes to be of good and approved quality, one and one-half inch, and over, being lap-welded pipe.

Fittings. All fittings to be of gray iron, heavy pattern, full thread, and of good and approved quality; no malleable iron fittings to be used on the work. All flow and return pipes in basement to be supported by neat, strong, and adjustable hangers, arranged to suit expansion and contraction, properly secured to timbers overhead.

At all points where pipes pass through ceilings, floors, or partitions, the channels or holes shall be protected with floor or ceiling plates.

Expansion Tank.-The expansion tank to be made of No. 22 galvanized iron, 25 inches high and 15 inches in diameter, and is to be furnished with a proper gauge glass, with brass mountings complete. It is to be placed above all the radiators, in some suitable place, and supported on a proper shelf. From this tank an overflow pipe will be run to basement or other suitable place. Furnish and set up the following radiators, viz.:

In all 380 square feet of direct surface and 165 square feet of indirect; total surface, 545 square feet.

Each radiator to be supplied with a (Gurney) Radiator Valve, brass seat, full opening, connected to flow-pipe of radiator.

Each radiator is to have a neat, nickel-plated air-valve on its highest point, made to open and close with a key wrench.

All radiators and exposed pipes above cellar to be neatly bronzed in gold or silver bronze, or artistically painted, as chosen.

No carpenter's work included.

All pipes in basement to be covered with one-inch hair felt, and neatly sewed up in canvas and painted one coat of good white lead.

The contractor to guarantee all materials and workmanship used in the construction of this apparatus to be the best of their respective kinds, and the apparatus to be complete, and capable of warming the rooms and halls in which radiators are placed to a temperature of degrees Fahr., when the thermometer is at zero outside.

Steam Heating.

Although hot water is perhaps more popular just now for residence heating, there can be no question that a building can be as thoroughly warmed and ventilated by steam as by any other system, and generally at a smaller first cost. In very cold weather, it is doubtful if hot-water heating is as satisfactory as steam.

For indirect radiation, steam heat is generally considered cheaper than hot-water heat, and in every way as satisfactory.

For very large residences, the author would recommend steam heat, all of the principal rooms to be heated by indirect radiation, and only the bathroom, halls, and perhaps the attic and one or two rooms on the north side, which generally includes the diningroom, by direct radiation. For dining-rooms a special direct radiator, containing a warming closet, is made.

The air supply to the indirect stacks should be very large, and provided with a damper, so that the supply may be regulated according to the weather. If the indirect radiators are divided into sections, each section being controlled by a valve, either one-half, one-third, or the whole of the radiator may be used at will. The greater the radiation the more fuel will be consumed, and vice versa, so that when part of the radiation is cut off, the cost of running the boiler is reduced.

The same principles apply in heating a residence by steam as in heating any other building, and there is no difference in the piping and radiators. The boilers used in residence heating, however, are generally of a special pattern, designed especially for that class of work.

There is almost an infinite variety of these boilers, although a great many of them are of the same type. The requirements of an economical and satisfactory working boiler for house heating are as follows:

First.-They should contain a quantity of water sufficiently large to fill the pipes and radiators with steam to any required pressure without lowering the water in the boiler to require an addition when steam is up; for should the steam go down suddenly, there will be too much water in the boiler. This occurs in boilers made with very small parts, or pipes which have a small capacity at the water-line, and require great care; for should the boiler have an automatic water feeder set for the true water line, it will fill up, but cannot discharge again when the steam goes down; while, if it has no feeder, there is danger of spoiling the boiler, as the water is in the pipes in the form of steam.