I need ideas on how to heat a chicken coop, housing 4 hens, in North Dakota Winters. We are the Siberia of the Northern Plains. Wind chills can get to -75F and normal temps as low as -50F. The coop we have is 8'Wx6'H16'L. I'm on SSDI and $$$ is ever so limited. I'm nearly 66 and do all outside chores myself. So I need economical advice.