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why the plumber connected the supply and return ends together
Two yrs ago, we did oil to gas conversion. In the same time, we moved the boiler from one room to another. The main line is 1" pipe. In the old layout, the ends of the return and supply was not connected. The plumber connected the ends together during the conversion. There is no other changes related to the existing pipes. There is no other device/valve attached to the individual CI baseboards. Please have the look at the diagrams attached, or big version here, http://www.flickr.com/photos/bostonjames1980/sets/72157629021634185/detail/. The old Oil boiler is located at top right corner and the new Gas boiler is located at the bottom left corner.
The boiler loop in the new setting is recommended by the Burnham installation manual.
My questions are what's the difference if the ends are connected and the ends are not connected? and are they both 2-pipes direct return heating system?