I’m revisiting this now that I put an order in for heaters. I went with 6,000 watt 240V heaters but they are dual element, 3,000 watt each element. I have a 10/3 line going from the breaker box to a switch, then to the heater. Each element should consume 12.5 amps at 240 volts. I’ve discovered that I can gain access to the wires going from the light switch to the heaters via an 8" ceiling speaker hole.
Could I use two Shelly Plus 1 devices, one for each heating element, between the switches and the heater? The switch is a duplex single-gang switch. One switch for each heating element. Will toggling the wall switch toggle on/off the Shelly and the heaters? Can I even get a 10 gauge wire in a Shelly terminal?