I have one 20 amp double pole circuit that I am planning to run 3 baseboard heaters on with 2 line voltage thermostats. I have already made sure the watt consumption for the 3 heaters will not exceed 3,840 watts. I have run 12/2 wiring from the breaker to the first thermostat location which will control 2 baseboard heaters and from there to the other thermostat which will control the 3rd heater. I have uploaded a quick diagram for visual reference. I believe I know how to correctly wire this up but just want a sanity check before committing. I believe I can just pig tail at thermostat 1 to pass power through to the second thermostat location (bedroom) and for the thermostat that controls two baseboard heaters, it seems like the wiring is simple. Any help is appreciated! 
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Good Prep, Plus One... – Harper Jun 5 '18 at 1:53
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You are correct -- just don't overstuff the box!
Pigtailing the wires to room 2 with the line-side of thermostat 1 will get you what you are after here. However, with the thermostat and the 3 12/2s in there, that's too much stuff for many single gang boxes (20.25 in3 of box fill vs the largest standard device box in the Code being 18in3), so you'll want to use a bigger box such as a 4" square with a single gang cover/mudring there instead. You'll also want to wrap each of the white wires in this with black tape to make it clear that they're hots, not neutrals.
