I have 2 electric 240v baseboard heaters w a single pole thermostat fed by a single 12/2 cable always hot. Purchased Honeywell double pole mechanical replacement - do I need to run another 12/2 or can I have a constant 110 leg to the heaters? Junction box has wires for 2 baseboards, hot 240 supply and feed to thermostat, all 12/2 w ground.
You can use the Honeywell, but you must put both poles in series. Only one pole is switched thermostatically, theother is switched mechanically(on off only).
So connect one wire of pole 1 to one wire of pole 2. Then connect the remaining wires to the ones coming from the wall.