I have an oil-fired boiler for heating the house. The hot water output goes to conventional radiators, plus a radiant floor system. The odd thing, to me, about this system is that the boiler output, besides branching off to the radiators and the radiant floor system, loops back directly into the cold-water return. This loop-back takes place immediately above the boiler, so the distance that some of the output hot water takes is only about 8 feets before it returns to the boiler via the cool-water return pipe. Thus the "cold-water" return pipe is just a hot as the hot-water pipe leaving the boiler (i.e., you can't touch it with your bare hands). There is a shut-off valve which can break this loop. I have asked some plumbers and some say that that is an efficiency issue, needed to prevent the boiler from having to heat up the fully heat-released return water; i.e., since the return water is hot, the boiler doesn't have to work as hard. This sounds true but nuts to me (and to some other plumbers), since much of the water is bypassing heating the house and is just cycling directly (and to me, pointlessly) back into the boiler.
Can anyone clarify if this makes sense (to have this immediate feedback), or can I safely eliminate this loop by using the shutoff valve?