Heatloss calcs

[irving2008]

And for reference, while googling I found this page with lots of R-values for various materials - R-value

Got to be careful with the U <-> R conversions. A lot of non-US sites give 'European' R values, i.e. 1/U, where R is (Kelvin m^2/W) per 25mm thickness. (mental note to self to go back and check my own calcs!)

So loss = U x A x Dt. For several layers, of materials having R-Values R1 - Rn of thicknesses t1 - tn, U = 1/(R1t1 + R2t2 + ... + Rntn) If all the R-values are US ones, then U = 5.682/(R1t1+R2t2+... +Rntn)

I used several sites, including this one: http://www.stronggreen.com/docs/R-Va...0Materials.pdf for R-values

That give R value for 8" concrete as 2, so 6" has R of 1.5 or U of 5.682/1.5 = 3.8, not the 2 you have used... so loss through the slab is higher at 36.75 * 3.8 * 10 = 1400W approx.

However this article from the concrete industry confuses it all by talking about U = 1/R when R is in the BTU form! Their figure gives a U factor, in SI units, of between 4.7 and 9.4!!!

This page was useful too: http://www.the-flat-roof.co.uk/Appendices.pdf


Just revisited your walls calculation. R = 0.2 per inch, so a 4" brick = 0.8, so U in SI units = 5.682/.8 = 7.1, so your heat loss through the walls is 7.1 * 53.9 * 20 = 7.6kW. I note your calc was 5 * 53.9 * 20 = 5.4kW, yet you wrote = 1347W ???