In fairness to all, we don't discuss pricing on the Wall. Thanks for your cooperation.
I did a load survey at a 2-story school from the 40's I think, and it is gravity hydronic. Every radiator on both floors was piped the same way, with the radiator as a bypass off a downcomer that came out of the ceiling and went into the floor. This system has evidently been running OK for 75 years or so, and I can't figure out why the radiators have flow. Oh, duh - I think I just got it. The cold water in the rad is heavier than the hot water in the pipe so it drains out and is replaced by hot water. I guess I asked the right guy. Anybody agree or disagree? Thanks for thinking about it.