ice forming on unit

I need to replace my current furnace and I'm looking for a german made oil furnace. I was told that they are more fuel efficient. I have been searching the web endlessly. Need help.

I have read through the forums, and have only found one that touches on my problem (but doesn't exactly answer it). We live in a 1-year-old split-foyer home. Of course, that means that the downstairs is 4' under ground, and is completely finished. Our furnace room is also downstairs, and is in a finished, insulated room. All of our ducts are contained in the walls and finished ceiling (which is insulated with sound batting). Most of the windows downstairs have a northern exposure, and most upstairs have a southern exposure. That, combined with the fact that half of the downstairs is underground, means that downstairs is much colder than upstairs. The thermostat is upstairs, and on sunny winter days, the heat doesn't seem to run enough to heat the downstairs well. Some of our bedrooms are upstairs, and some are downstairs, so that creates a problem for my children! They are little blue icicles! :) We have closed (not all the way) some of the dampers in the rooms that are closer to the thermostat. Those rooms happen to be bathrooms and closets with no windows, meaning they are way toasty. Unfortunately, the upstairs and downstairs are fed by the same ducts, so the upstairs rooms are comfy now, but the downstairs rooms are freezing. Any advice?? (Of course, we have the opposite problem in the summer with the A/C.)