Upgrading baseboard thermostat -wiring help
I think I just need to separate the nuts connecting the white wires from the line in and run that to the new stat, leave the two white load lines and connect those to the load out of the double pole but wanted to make sure.


Short answer is: Yes, you can do that or you can just use one set of wires like they did. (The National Electrical Code does require a disconnect for the heater. The thermostat can be used for this as long as it disconnects both ungrounded conductors and has a marked "off" position.)

Long answer is: Whether you use a single pole or double pole thermostat it will work the same. It is a single phase circuit and it will work either way.

The difference is, with a double pole thermostat you are breaking the circuit in two places at the same time instead of one. This reduces the amount of pitting on the device contacts. With a double-break device the contacts will last longer at any given voltage. At 240 volts contact pitting is much higher than at 120 volts.

If you had a triac based thermostat contact pitting becomes a non-issue and you can go back to breaking the circuit in one place.

Good luck!