Direct Hot-Water Heating

In flats of eight or ten rooms, the size of the last radiator may be increased from 10 to 15 per cent, and the intermediate ones propor tionally, at the same time keeping the main of a large and uniform size for the entire circuit.

Overhead Distribution.

This system of piping is shown in Fig. 90. A single riser is carried directly to the expansion tank, from which branches are taken to supply the various drops to which the radiators are connected. An important advantage in connection with this system is that the air rises at once to theaexpansion tank, and escapes through the vent, so that air-valves are not required on the radiators.

At the same time, it has the disadvantage that the water in the tank is under less pressure than in the heater; hence it will boil at a lower temperature. No trouble will be experienced from this, ever, unless the temperature of the water is raised above 212 degrees. Expansion Tank. Every system for hot-water heating should be connected with an expansion tank placed at a point somewhat above the highest radiator. The tank must in every case be connected to a line of piping which cannot by any possible means be shut off from the boiler. When water is heated, it expands a certain amount, depending upon the temperature to which it is raised; and a tank or reservoir should always be provided to care for this increase in volume.

Expansion tanks are usually made of heavy galvanized iron of one of the forms shown in Figs. 91 and 92, the latter form being used where the headroom is limited. The connection from the heating system enters the bottom of the tank, and an open vent pipe is taken from the top. An overflow connected with a sink or drain-pipe should be provided. Connections should be made with the water supply both at the boiler and at the expansion tank, the former to be used when first filling the system, as by this means all air is driven from the bot tom upward and is discharged through the vent at the expansion tank. Water that is added after ward may be supplied directly to the expansion tank, where the water-line can be noted in the gauge-glass.

A ball-cock is sometimes arranged to keep the water-line in the tank at a constant level.

An altitude gauge is often placed in the base ment with the col ored hand or point er set to indicate the normal water line in the expan sion tank. When the movable hand falls below the fixed one, more water may be added, as required, through the supply pipe at the boiler.

When the tank is placed in an attic or roof space where there is danger of freezing, the expansion pipe may be connected into the side of the tank, 6 or 8 inches from the bottom, and a circulation pipe taken from the lower part and connected with the return from an upper floor radiator. This produces a slow circulation through the tank, and keeps the water warm.

The size of the expansion tank depends upon the volume of water contained in the system, and on the temperature to which it is heated. The following rule for computing the capacity of the tank may be used with satisfactory results: Square feet of radiation, divided by 40, equals required capacity of tank in gallons.

Air-Venting.

One very important point to be kept in mind in the design of a hot-water system, is the removal of air from the pipes and radiators. When the water in the boiler is heated, the air it contains forms into small bubbles which rise to the highest points of the system.

In the arrangement shown in Fig. 88, the main and branches grade upward from the boiler, so that the air finds its way into the radiators, from which it may be drawn off by means of the air-valves.

A better plan is that shown in Fig. 89. In this case the expan sion pipe is taken directly off the top of the main over the boiler, so that the larger part of the air rises directly to the expansion tank and escapes through the vent pipe. The same action takes place in the overhead system shown in Fig. 90, where the top of the main riser is connected with the tank. Every high point in the system and every radiator, except in the downward system with top supply con nection, should be provided with an air-valve.

Pipe Connections.

There are various methods of connecting the radiators with the mains and risers. Fig. 93 shows a radiator connected with the horizontal flow and return mains, which are located below the floor. The manner of connecting with a vertical riser and return drop is shown in Fig. 94. As the water tends to flow to the highest point, the radiators on the lower floors should be favored by making the connection at the top of the riser and taking the pipe for the upper floors from the side as shown. Fig. 95 illus trates the manner of connecting with a radiator on an upper floor where the supply is connected at the top of the radiator.