Welcome aboard Oldschool.The system you are talking about,either by natural convection or mechanical means is a simple install on a new constuction setting but is a little tougher in an existing structure.I suspect that hot water lines will freeze faster becuase the minerals in the hot water in the house have "settled" in the holding tank and are more pure than the cold water.I'm sure my brother (aplumma) will have the correct explanation for this.I do know that the first lines to freeze up in a house are the hot water lines from almost 30 years of plumbing work.I always like to see a lurker finally post here.Cheers!
Joe