My idea of cold is single digits or below - I think that's when it will be a challenge for the NAH to heat the cabin and still run in the EV mode.

I did some checking around - there's lots of info on the Prius out there. The Prius has an electric water pump so coolant will still circulate when in the EV mode. There are also a couple of electric heaters in the heater core so heat will be avaiable before the coolant gets up to temperature. I have no idea if these features are in included in the NAH or the TCH. I would think if the Camry has it then the Nissan would as well seeing how they used the rest of the THS.

I believe that the Prius system requires the use of an automatic climate control for the system to work properly. That could be the reason Nissan included the automatic climate control system as standard equipment in the Hybrid and therefore there's a good chance that there are electric heaters and an electric water pump as well.