I dont have any zone valves, so no problem there, just a circulator pump and 25 Ft of cast iron radiators at $140 a foot to replace.As I think I mentioned earlier, antifreeze is a good solution for some installations, but the tradeoff is that it tends to gum up or corrode zone valves a little faster than plain water. I use it, so not saying it's a bad idea, just that it ain't no free lunch (as with most things in life).
-dan