[Greenbuilding] Slab heat loss calculation

[nick pine]

Alan Abrams <alan at abramsdesignbuild.com> wrote:

> the Current Project calls for 9" of subslab geofoam rated at R-4.2 per 
> inch, and clocks in with a specific space heat demand of 4.75 
> Btus/SF/year. The house contains 1735 SF of *treated* floor area...

4.75x1735 = 8421 Btu/year, ie 8421/100K = 0.0824 therms per year.

> changing to 2" of foam increases the SSHD to 5.90 Btus/SF/year, requiring 
> about 20 additional therms of natural gas to make up the difference.

5.90x1735 = 10237 Btu/year, ie 10237/100K = 0.102 therms per year.

Nick