I know an old guy who uses "solar" heating. He has a South-facing
hangar, and has painted the doors black. So the sun warms the hangar
when it's cold out. When it isn't cold, he opens the doors - how much
depends on the temperature. He also has a false cieling of
plastic sheeting to keep the heat from rising to the top. Of course he
is retired, and spends nearly every day there - so he is the "manual"
thermostat.

As for critters, he keeps a 22 rifle with birdshot shells handy - and
doesn't hesitate to use it.