178 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 39 



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Figure 9. — Absorber piping diagram for three pipes In parallel. 



outside; (9) paint black all over; and (10) glaze in accordance with 

 regular skylight practice. 



Removable glazed cover. — The glazed frames must be removable 

 for spring cleaning of the under side of the glass and for servicing 

 the pipes or tanks in case of trouble. It is also desirable to place the 

 solar heater in front of an attic window to facilitate cleaning of the 

 outside surface, which in some localities should be done as often as 

 once a month. 



The shape of the absorber depends upon the glass sash used. 

 Hotbed sash 3x6 feet is the cheapest but has considerable wood area ; 

 four sashes would be needed for a 60-gallon system. If the absorber 

 box can be long, single-light window sash 18 x 48 inches can be used, 

 12 being required for a 60-gallon system. In this case the puttying 

 at the bottom must be brought up on the glass far enough to drain 

 off the water when the window sash is in its sloped position. In all 

 cases the pipe must rise continuously from the drain to the storage 

 tank. Any dip in the absorber coils will form an air pocket and 

 seriously interfere with the thermosiphon circulation. 



Parallel-pipe absorher coils. — The common pipe absorber is a zig- 

 zag of %-inch pipe, and this is suitable for small solar heaters. If 



