off the grid.....sounds like a quote from the movie tropic thunder.... didn't end the way it was planned .... depends what your definition of "off the grid" is ...does it mean land mine infested jungles, Antarctica, or just family camping in a campgrounds?
I'm assuming you don't have central heating of some kind...
We don't run heat in the winter. Right now it's about 65* in here. The birds are fine all day but at night we put a space heater a few feet from their cages and they seem to do just fine.
Then again, this is AZ and our cold is definitely not your cold :/
Having an insulated area, protected from drafts is the biggest thing, if not where the cage is normally located, a seperate "roosting" area for night time. Birds can adapt, but it's a sudden change in temperature that can do harm. I'd suggest increasing good fats in the diet to help maintain body fat and core temperature, as well as feeding some warm meals if possible.
Other than that, be careful of smoke if you use a fireplace, maybe heating water for a hot water bottle near the cage would be an option as well.
~Alexandrine Parakeet~2 Red Lored Amazons~Blue Fronted Amazon~Black capped conure~4 Green Cheeks~4 Parrotlets~2 lineolated parakeets~9 American budgies~9 English budgies~ And lots of babies :)
We heat our house entirely by woodstove. It can definitely be tedious but it is nice for those times when the power is out and everyone else is losing their minds because they don't have heat. Insulate well and source any drafts. If you have a woodstove, which I assume you do, make sure the damper is open whenever you open the doors so no smoke escapes into your house. Also only burn safe wood, nothing pressure treated or painted. You may also consider covering or partially covering your birds cages at night.