If I update the HDD to cover the Oct. 17th - Nov 19th I get 809. With an annual 5570 HDD, that works out to 4634 gallon or $11,121. It would be interesting to know how that compares to the gallons used last year.
Using the updated numbers, heat loss for the building is 3172 BTU/H/Deg.
199,000 BTU/H / 3172 BTU/H/Deg = 62.7F delta to run out of capacity.
Coeur D'Alene Airport is used as the location for Bonner and has a 99% design temp of +10F. No capacity issues if that is true. OP has been through one winter, so they can let us know if they ever weren't able to maintain the 60F setpoint. Someone more knowledge of the local area could likely pick a better reference:
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This is a load calc using actual fuel use, which is generally accurate at predicting total fuel use. It will also provide an accurate capacity estimate without the overestimate seen from of sq ft * DT/ R.
If I assume the enclosure is performing at the table listed total wall R Value of 7.2 and using the updated floor load, I get that you would need about 900cfm of infiltration to match the fuel usage based actual BTU consumption. That is a LOT, but not unheard of. But ton of infiltration along with some missing insulation in areas like a stem wall would do it. Increasing the
total wall R value will result in significant savings, particularly because the smart approaches will also address infiltration. The focus on total wall is super important, 4x insulation in the bays will barely move the needle.
It is still worth checking for weird things like leaks in the loops. I would also review where the moisture barrier was placed relative to the sub slab foam. If they happened to place it below the foam, the slab can be sitting in a bathtub. Putting the plastic below the foam makes it seem like the foam will stay dry, but it instead it traps water in the foam.
Regardless of any calculation details, it is clear this building is pissing away fuel. We aren't going to fix this here though other than to push that they need someone who can analyze the situation on site. There are just too many things to cover. A blower door will give the real infiltration load, identify the major leak sources, and spot major thermal issues.
I believe code compliance still may be required where the OP is, even if there are no inspection. It is the builder's responsibility to ensure code compliance (at least where I am), so there might be some avenue for legal action. I would imagine the builder would only be responsible for the additional remediation costs beyond what it would have cost to build it right the first time, so it may not be cost effective.