Heaterman, Pete and Ihookem- I think you all make some good points here.
Some things that stand out to me-
Unfortunately a 2x6 wall with 2 lb CC SPF is not going perform as an R33 wall. The thermal bridging of a 20% framing factor is going to bring the whole wall R value down significantly. And a 25% framing factor is more likely. The biggest advantage of foaming between studs is the air sealing and that is some expensive air sealing. Here is a much better explanation than I can give:
http://www.greenbuildingadvisor.com...o-help/26996/maximum-insulation-thinnest-wall (post #5 in particular)
Now, a few inches of continuous insulation outside of the sheathing, with lower cost cavity insulation (cellulose is ideal for its cost and moisture buffering capacity) can give a much better bang for the buck and achieve a whole wall R value of 30+ depending on the material selected. On my folks house I have used reclaimed commercial roofing insulation(polyiso) from insulationdepot.com. This material cost us .65 $/ft for 2.5"(R15) delivered.
Now lets look at some numbers. Ihookem figures 25k btus at a design temp of -10
![Fahr ::F ::F](/talk/styles/default/xenforo/smileys/f.png)
. Using the degree day method for estimating annual heating energy shows he would need about 33MM btus/yr+ DHW(I'll guess 10MM btus for DHW) so 43MM btus/yr and he is burning 3.5 to 4 cords a year. I've got to think his EKO 25 is getting more than 11 to 12MM btus out of a cord of wood, even without storage, but it all depends. I'd guess his heat load is more like 40k btus at design temp and this would mean he would need about 50MM btus/yr+10MM btus for DHW. Seems more realistic given the 3.5 to 4 cords he is burning. Not bad numbers at all though he mentions in his sig that the $9400 he has into his EKO install is "still too much$" and I tend to agree. For my folks house I am putting that kind of "extra" money into the enclosure to get the heat load as low as reasonably possible so they can heat the house with a wood stove and a cord or so of mixed hardwood.
Every situation is different. And I understand heating multiple buildings gets tricky, and gassers+storage and low temp emitters are a great but expensive way to do the job. Another option is to build super insulated, reasonably air tight houses with quality windows that don't need the kind of heat distribution systems to achieve comfort that "to code" houses need. And the bonus is minimal effort/expense to be comfy.
With new construction, you basically get to pick how much energy you want to use for many years to come, as well as future generations. That is why I recommended an energy consultant to the OP.
Eliminate the guess work or just wing it, either way we all get to live with our decisions, as it should be.
Noah