My house is ICF construction, our walls are 12"thick.
http://www.buildblock.com/?gclid=CImUzfnEu7ICFad7QgodozoAUQ
Our utility bills are less than our neighbors with half the square footage we have. During the summer, our home will stay 78 degrees or below even when the temps hit over 100. I have had the home for near 3 years and have turned on the central AC 3 times, mostly to make sure it was still working. As for windows, we have energy efficient windows and have added double honeycomb binds behind our insulating drapes. The attic has been insulated to Energy star ratings as well. We are pretty close to being an Energy Star home. The floor of the basement is not insulated, but unlike our other homes with a basement, oddly the floor is never cold in this one. We do have area rugs over quite a bit of the floor though. As far as putting a second stove in, we have given it some thought. But if you look up how the home was built, anything that is on the inside that needs to go outside really needed to be in place when the concrete was poured into the walls.
To have holes cut through concrete/rebar is pretty tough and the Styrofoam has to be cut quite a bit away to keep it from melting.
As I said, the Englander comes close. It keeps the house warm, I can not remember at what temperature, but in the 70's I am just looking to see if the other stoves are more efficient with longer burn times. BTW, the stove is in the basement, working with the heat rising
edited to add...yeah, 18'celing in the main room on the main floor

but it opens up right into the upper level