[Greenbuilding] Slab heat loss calculation

Norbert Senf mheat at mha-net.org
Mon Aug 26 18:57:35 CDT 2013


For 2" foam, the original ballpark of 100 lbs of 
wood per year for 900 sq. ft. would be 192 lbs for 1735 sq.ft.

Using Nick's numbers, the computer modelling 
works out to 158 lbs instead of 192, or about $12.00 worth of firewood.

Norbert

At 06:41 PM 8/26/2013 -0400, Alan Abrams wrote:
>sorry, that should be 4.75 kiloBTU's/SF/yr, etc...
>
>AA
>
>
>On Mon, Aug 26, 2013 at 5:40 PM, nick pine 
><<mailto:nick at early.com>nick at early.com> wrote:
>Alan Abrams 
><<mailto:alan at abramsdesignbuild.com>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
>
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>--
>Alan Abrams
>certified professional building designer, AIBD
>certified passive house consultant, PHIUS
>certified passive house builder, PHIUS
>Abrams Design Build LLC
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-------------------------------------------
Norbert Senf---------- mheat(at)heatkit.com
Masonry Stove Builders
25 Brouse Rd.
RR 5, Shawville------- www.heatkit.com
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