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92 although if the flues are of considerable length or are winding, a larger ratio should be given. If a number of radiators receive air from the same cold-air flue, the flue may be somewhat smaller.

Figure 47.—The Indirect System in a Massachusetts Residence.

In buildings in which there are a considerable number of indirect radiators there are two general methods of connecting the fresh-air flues, which are illustrated in Figures 47 and 48. Figure 47 represents the cellar plan of a large Massachusetts residence (The Engineering Record, August 5, 1893; Mr. A. A. Sanborn, Boston, heating contractor), in which there are seven large clusters of indirect radiators which supply about 30 hot-air flues rising to the rooms above, the hot-air pipes running horizontally from the radiator boxes, in some cases for 50 feet, to the vertical flues. radiators in this are all Gold's Pin in 16-foot sections.) In the Philadelphia residence shown in Figure 48 (The Engineering Record, December 15, 1894), there is, on the contrary, a long main cold-air duct which supplies a large number of indirect radiators, one for each of the vertical flues, the radiator in all cases being located directly under the vertical flues. In the opinion of the author this is much the preferable method,