Posted By Jeff from KY on 03 Mar 2010 03:00 PM
Quick question on wall R values. Our house is also earth sheltered. Approximately half of the walls are 10" thick poured concrete with 2" of rigid foam insulation on the outside, with all except the top 18" underground. Should I use an R value of 10 (just the foam) or should I increase the R value for the concrete and the earth sheltering? Thanks.

Since the cold-side of the foam is dirt at a relatively constant temp closer to the average annual air temp at the bottom, maybe close to the seasonal average temp at the top, it won't be anything LIKE the heat loss against your design-day outdoor air temp of (guessing here) 5-10F.  from a modeling point of view it's probably closer to treat the earth sheltered wall surfaces as if they were insulated slab rather than wall.   It's 40-55F dirt you're insulated against on those sides not 5F air, and it'll be a small fraction of the total heat loss.

I would think that a good heat loss calculator would have you enter the % of the wall that is below grade. It would need this capability for determining basement heat loss. You wouldn't adjust the wall R value.

Thanks, guys. Good points and thoughts. As I said at the start, I will eventually have a professional heat loss and design done, so this info is plenty good for my first cut.

Well we met up with the GC and none of the Heating Contractors has submitted a bid. One of them commented that we would need 1 mbtu?

So the saga continues.

I do now have a contact with a specialist who works with our GEO. Should see him week after next.

http://www.hillsideenergy.com/calculators.htm

Another calculator

This one for me was just over 400,000.