Thanks for all the advice to date.... Based on the advice received, I am going to go with a thermostatic mixing valve, variable speed circulator and zone valves from storage. I have been looking at mixing valves and am having trouble sourcing one of the right size for less than a fortune. I have 1-1/2" supply and return lines from storage (about 24 gpm total to 5 zones) and while I can find 1" TMV's all day for $100-$150, the cheapest 1-1/2" valve I can find is over $500. Maybe I should think about using 2 smaller circulators (taco bumblbees look nice) and two smaller, 1" TMVs, spliting my zones into 2 parallel loops...? Anyone have any recommendations for a reasonably priced 1-1/2" TMV?