This might sound crazy. installing solar panels where it doesn't snow of course, connecting to deep cycle batteries, a power inverter to run your hearth fan?
I was thinking about doing the same thing to run the fan on my wood furnace but i have no idea where to start. Harbor Freight sells 45 watt solar panels for $130 i have been thinking about trying but i don't know if that'd be enough to charge a battery bank to run the fans. Keep us posted if you do it.