I have a Laars gas boiler that has 3 heating zones; basement, 1st floor, and 2nd floor.  I want to replace the old mercury honeywell tstats on the 1st and 2nd floor with newer honeywell RTH9580 wifi model for both. The 2nd floor is a piece of cake as the current tstat and wiring there also consists of the central cooling control.  So on the 2nd floor I have all the necessary wires for the new tstat there to work with (red, white, yellow, green, and blue).  On the 1st floor however, the current tstat only controls the heat, and there is only the 2 wires, red and white. I have a clear shot to the basement in the wall behind the 1st floor tstat, and can run new wires from there to the boiler, no problem.  My dilemma...once I get the wires there (and do I run 5 wires and just use the red, white, and blue?), how do I hook up the blue wire?  To the boiler itself?  To the wires connected to the zone valves, and which one? Or to the transformer, and how?  I've taken pictures of my entire system, can someone tell me the best method (proper preferred, not necessarily easiest) to accomplish this? 

I've added some more pics to included the transformer specs and the boiler schematic















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