I just renovated my basement. Installed 12-2 wire and installing 2 convection heaters (2000 and 1500) watts to my Thermostat. The current config is form my electrical panel, 20 amp breaker, the 12-2 wire goes to the first heater 2000 watt then to the Thermostat then to the 1500 watt heater. The problem I have is that the 2000 barely gives off heat and the 1500 give off some heat. I checked to make sure I was getting the full 240 volts from the panel. Don't know where the problem is?

Is it a 2 pole 20 amp 240 volt breaker?

Do you have 240 volts across both poles?

Do you have 240 volts at the first thermostat?

Second stat?

Yes it is a 2 pole 20 amp 240 volt breaker. When I testes the voltage I received 120 form the black and 120 form the red wires. IF I put them together I get 240. The 12-2 wire has one black, red and ground wire. My convection heaters have a black, white and green/yellow ground wire. I

The first configuration is form the 12-2 panel wire I connect the blk to the blk form the heater. Then from the white to the black on my scond 12-2 wire which is going to the thermostat. I connected the 2 red wires together and the ground to ground wire.