I will verify with Atwood, but I believe IF the system CANNOT see the coil of the Gas Valve, the system will not fire on 120. The reason I state this is, the ECO is ONLY connected to the Gas Valve solenoid and the 120 side cannot stop if the unit overheats(stuck Tstat) and the ECO opens the circuit. Once the ECO opens the circuit, the Board cannot see the Gas Valve coil and trips and stops all operation. Doug
PS, I understand now since you clarified about the heat. IMO, you are overthinking that heat. True convection draws from below and exits at the top. On an Atwood the intake is just below the exhaust and the cold air would have to enter and then go downward before entering the flue and coming back out the top. Negligible loss.
