Attic Heat Recycling
 

"Heat energy builds up inside your attic -- even on winter days with chilly temperatures. The SolarAttic Space Heater takes this free renewable solar heat from the peak of your attic and supplies it to the interior of your home."
https://www.solarattic.com/space.htm

For more power, add an air source heat pump
https://www.freepatentsonline.com/4254822.html

I like this idea. I wonder
 

I like this idea. I wonder how hot it does get in the attic. Perhaps I'll run an electric thermostat up there to find out.