This section is from the book "Cyclopedia Of Architecture, Carpentry, And Building", by James C. et al. Also available from Amazon: Cyclopedia Of Architecture, Carpentry And Building.
The heaters for indirect hot water heating are of the same general form as those used for steam. The heaters shown in Fig.. 9, 14 and 15 of Part I, are common patterns. The "drum pin," Fig. 14, is an excellent form, as the method of making the connections insures a uniform distribution of water through the stack. Fig. 51 shows a section of good form for water circulation, and also of good depth, which is a necessary point in the design of hot water heaters. They should not be less than 10 or 12 inches for good results. Box coils of the form given for steam may also be used, provided the connections for supply and return are made of good size.
As indirect hot water heaters are used principally in the warming of dwelling houses, and in combination with direct radiation, the easiest method is to compute the surfaces required for direct radiation and multiply these results by 1.5 for pin radiators of good depth. For other forms the factor should vary from 1.5 to 2, depending upon the depth and proportion of free area for air flow between the sections.