I use a natural gas, gravity flow, wall furnace in a vacation home. It
runs on natural gas alone. Absolutely NO electric to the furnace
whatsoever.

The thermostat is controlled by a "millivolts" charge that are
generated by the pilot light.

The one I use is installed in a wall, (between two studs), and provides
heat into two rooms as heat is given off from the front and the rear
panel. It is approximately 55,000 btus.

It is a "Cozy Wall Furnace" and manufactured by "Louisville Stove Co.".

They are relatively inexpensive and easy to install and best of all NO
reliance on electricity.