Warm a Room with Only a Candle and a Few Terra Cotta Pots.The terra cotta pots concentrate the heat using convection. While you won’t heat a whole house with it, it can definitely warm your hands and make a cold night much more bearable .
Did you know, you can use common bubble wrap as insulation for windows? I had heard of this bubble wrap trick to save energy before, but had never actually gotten around to trying it. Not for every window, but just an idea to consider.