once drawn as hot as branches taken off the flow pipe will deliver. Above the boiler a branch connection is taken out of the main flow pipe to serve fixtures in other parts of the house on the two floors above the boiler. After passing the last fixture on the third floor, the circulation pipe B is connected and carried down, being entered into the return or circulation pipe from the first line.

Circulation Pipe

FIG. 290.-The Three-tube Boiler.

For fixtures below the boiler a branch is taken out of one of the flow lines and carried down to the desired points. Circulation cannot be provided for these fixtures because of their position as related to that of the boiler. Therefore, in obtaining hot water at the laundry tubs, it will generally be necessary to draw off the cold water standing in the greater part of the length of pipe running to this fixture. In connection with the work thus far illustrated,

the return or circulation pipe has in each case been carried back into the return of the range connection. This is ordinarily the method followed. In the use of the three-tube boiler another and neater method may be employed. This method is shown in Fig. 290. In the three-tube boiler a second boiler tube may be used, which should run down to a point near the bottom of the boiler,

as in the case of the boiler tube used on the boiler supply. To this second tube, the circulating pipe may be connected as shown, which results in returning the cooled water as well as by means of the connection into the return of the range connection. This illustration will also serve to show the manner in which circulation may be provided for fixtures on the same floor as the boiler. This is accomplished, generally, by running the flow pipe

from the boiler horizontally, on the ceiling, above the points where the fixtures to be supplied are located, and dropping from this main flow pipe with branches to the several fixtures. From a point just beyond the branch to the farthest fixture a circulation pipe is carried back to the boiler and connected to the return of the range connection. This is the best that can be done toward securing circulation for fixtures thus located. Necessarily, the cold water must be drawn out of the branch from the main to the fixture before the water will come hot, but even so, the use of circulation under these circumstances will be found to be of benefit. Another method of providing circulation for fixtures on the same floor as the range boiler will be seen in Fig. 288. In this method, instead of running the circulation pipe back to the boiler, just below and parallel to the flow pipe, it is dropped down from the ceiling to a point considerably below, and then carried horizontally back to the range return.

In this method, branches to fixtures may be dropped down from the flow pipe on the ceiling, or taken out of the circulation pipe. While the use of circulation in connection with large hotwater supply systems is a matter of considerable additional expense, in applying it to many small systems, such as commonly found in small residences, cottage houses, etc., where the plumbing is usually centralized, it often means the use of only a very small amount of additional piping. This fact may be seen by reference to Fig. 291, in which circulation is applied to the fixtures of the entire house, by the running of a comparatively small length of pipe. In the foregoing illustrations, circulation has been shown in connection with direct pressure systems only. In Fig. 292 is shown a tank-pressure circulating system of hot-water supply for a residence. There is no material difference in the work, except the use of an expansion pipe on the tank-pressure system. Fig. 292 shows the range boiler heated by means of both kitchen range and gas range, a very common combination.

In Fig. 293 is illustrated a tank system of hot-water supply, without the use of circulating pipes. A comparison of the two illustrations should prove conclusively to the student the practical advantages of circulation and the great saving in water bills following its use.

Jark