I built a new house about 3 years ago. The insulation sweet spot resulted in a heat loss of 13,000 BTUH for a 1300 SF house at -20 F outside and 70 F inside. The next level of insulation would have cut the gas bill by $50 per year at a cost of $12,000. There was no real in-between amount of insulation, and the job was already over budget. No savings in the heating system, either.
I really wanted the U-0.20 or better windows, but the extra cost was prohibitive. I did get a house that cools down at 1 deg F per hour when it's 0 deg F outside. That, along with the woodstove, means that a furnace failure is merely an inconvenience.
And, yes, I'm a mechanical engineer. If money was no object, I would have put in the better windows and extra insulation.
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