My mother lives in the Denver area. My father had quality storm windows and doors and insulation well over the norm (R30+ in the roof, I'm not sure about the walls) installed. The home has no noticeable drafts or cold spots. My mother has apparently had representatives from several companies, including the local utility, out to give her estimates. While her current furnace is 150,000 BTU, it is old and she has been told by everyone that she doesn't need that capacity (I presume because efficiencies have improved greatly). It does not seem that anyone has done a calculation. I read your messages to her so she could request the steps you mentioned. She is 78 and may not be in the house more than a few more years so that affects her motivation. At this point, she is leaning to a two-stage approx. 100,000 BTU Rheem. I have not yet checked out the software mentioned, but I plan to. However, she seems to be close to deciding on the Rheem. I am hoping she will still request the calculations be done.