I would seriously look at a corn burner, and some insulation. Corn is CHEAP and produces more heat per pound than coal. I am heating my house with one and it'e the bomb. You are in the corn belt so finding corn will not be hard.
And they also have a corn boiler if your house is anywhere...
Skinner, it really depends on how much yout in and out. A garage is not like a house. A garage door may be 75% or one wall and the amount of air turned over when you open it is significant. a 250K in that respect is not going to be oversized if yoyuu are using the garage as a garage. It will...