HOT-WATER PIPING Heater Connections. Where only one heater is used, the con nections are practically the same as for steam heating, except that no check-valves are used.
Where two boilers are to be connected and arranged to be run independently or together, valves must be inserted somewhat as shown by the plan view represented in Fig. 99. It is important that safety valves be used with this arrangement, as, in case one boiler is shut down and then fired up without opening the stop-valves, the pressure due to the expanding water will burst the heater.
Single-Main System. The single-main system, arranged some what like the circuit system in steam heating, is sometimes employed for hot-water heating. Fig. 100 shows the arrangement of this sys tem. The supply branches are taken from the top of the main, where the water is hottest; and the returns are connected at the side, the cooler water pass ing along the lower portion of the pipe back to the heater. On systems of con siderable size, this arrange "went of piping causes the water in the supply main to cool more rapidly as the dis ance from the heater increases than in systems where the supply and return water are kept separate.
System. With the two-pipe up-feed system, the pipes should be pitched up from the boiler 1 inch in 10 feet, if possible. Pockets in which air can collect must be avoided, as air will cut off the flow as much as a solid substance in the pipe would do. In the basement, the branches near the boiler should be taken from the side of the flow main, in order to favor the branches farther away, which should be taken from the top of the main. First-floor radiators should be given the preference, as to ease of flow in their connections, over riser connections with the floors above. If possible, feed the last first-floor radiator on a line before branching to riser. Fig. 101 illustrates the above points.
Keep the mains near the ends of long runs ample in size, even if somewhat larger than stated in the table, if runs are long and crooked.
No chances should be taken in regard to insuring the proper circulation of water in the system. Use no horizontal pipe smaller than 11-inch. Return mains pitch in the same direction as the flow pipes, and are generally paired with them, the connections being made on the side as shown in Fig. 102, or at an angle of 45 degrees.
The risers should be arranged to favor the radiators on the lower floors, since the water tends to rise and pass by the lower radiators. Distributing fittings, as shown in Fig. 103, are often used for this purpose, or the pipes may be ranged as shown in Fig. 104. Some labor is saved by the use of the special fittings described. Overhead-Feed System. Where attic space is available, the overhead-feed system sents certain advantages over the two-pipe up-feed method of ing. In residences, single risers are used, these serving for both supply and return, the water entering the top of the radiator and flowing back into the same riser from the lower opening in the radiator. No air-valves are necessary, all air passing up the risers and out through the vent, on the expansion tank. The overhead mains are connected with a rising main large enough to supply all the surface; these mains may be run around the building near the walls, as in the one-pipe steam circuit system; or may be carried down the middle of the building, with long branches extending to the risers near the walls, it being assumed that the radiators will be located near the exposed parts of the building.
The mains and branches should pitch down toward the risers, permitting the air to escape freely to the expansion tank (see Fig. 105). Special care should be used in hot-water heating, to secure an easy flow. The ends of the pipes should be reamed, and long-turn fittings used for first-class work, although, if the piping is generously proportioned, standard fittings will answer. A hot-water ter should always be placed on the boiler or near it, in the flow-main.