I have correctly wired a single 240v heater from a thermostat in my home, but in my cottage I wish to control several baseboard heaters with a single wall thermostat. In a 240v 20-amp circuit, I understand that 80% of max is the norm, i.e. 3750 watts and 16 amps...correct? Use 12-2 gauge wire right?

But what I am confused about is the difference between "series" and "parallel" wiring. I believe that multiple baseboard heaters must be wired with "parallel" wiring. Please confirm.

A BLACK and WHITE wire enter the first heater from the thermostat. A BLACK and WHITE wire will be there from the 1st heater, and a BLACK and WHITE wire from the next (2nd) heater via a length of wire. I imagine your instruction would also apply to the 3rd and 4th heater wiring which will of course be calcualted properly in terms of wattage and amperage as explained above.

Not sure how to wire them. My guess is to pigtail the white and black wires from the thermostat to the same color wires from the 1st and 2nd heaters. Am I correct. Thinking that would be parallel wiring.

Series wiring (which is wrong - correct) would be what, connecting one thermostat wire to the black wire from the 1st heater, and making a large "loop" of black to black, and black to white back to the 1st heater and to the thermostat white. I realize that a piece of black tape is required on the white wires as they will be hot.

It's probably simple, but I don't want to do this wrong.

Also, how are thermostats rated for a 20-amp double pole circuit? Is there some kind of calculation needed just like the 80% rule above for its rated value?

Thanks for your advice.

Much appreciated.