In the event of a power failure I believe (as long as it's not packed with wood) that it would naturally siphon/circulate the heat. I am very aware when it's operating and if it happens when I'm home I start the genset until the power comes back on. If it has been several hours since I loaded it I usually don't worry about getting up and starting the genny.
The heat duck comes right off the top, there really isn't a plenum in the normal sense.
I could rig up a battery back up as this time I used a 12 ga extension cord and just plugged it in in the basement.
