That's too simple. One must consider surface area, not volume. But the valid idea behind what you are saying is this: A furnace will have to be able to keep the living conditions inside comfortable. Sixteen degrees C inside is not comfortable. And that is only with 0 C temperatures outside. Recently it has been much colder than that, and a furnace needs to respond to this and provide the capacity for toasty temperatures inside a residential house when it is -20C outside. So yes Lowes' recommendation is correct.
That still doesn't answer my basic question -- how is the heat pushed out to the room? One poster above commented that the Blue Box we saw is just an exemplar not the one running. But the exemplar still didn't have any ducting connections, so is all the heat supposed to come out through the samovar to heat the room? Can one of the engineers here figure out how hot the samovar would have to be to heat 42,000 cubic feet? I would suspect incredibly hot and dangerous to touch or be close to. Secondly, without any ducting, wouldn't the air nearest the samovar be much hotter than the air at the farthest reach? And without ducting leading to floor and/or low wall radiators or vents, wouldn't most of the warm air rise to the top?
And, also too (I am aware of all internet protocols -- and if you don't understand this reference google it), the only wires I saw coming out of the blue box, and I could be wrong, were the 110 wire, with no wires leading to external thermostats. If the thermostat is incorporated into the blue box, then in order to ensure that the farthest reaches of the room are warm the thermostat would have to be set extremely high, making any areas near the blue box uncomfortable and/or dangerous. Yet you have to physically touch the blue box to adjust the thermostat or to hit the big red emergency button.
All of these simple everyday issues that have actually nothing to do with how the insides of Rossi's widget works shows me that the blue box and everything associated with it is a load of crap. That is not a functioning heater.