The unit thermal resistances (R-values) of both 40-mm and 90-mm vertical air spaces are given in Table 3–9 to be 0.22 m² · C/W, which implies that more than doubling the thickness of air space in a wall has no effect on heat transfer through the wall. Do you think this is a typing error? Explain.

Table 3–9

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Posi- tion Direc- tion of Heat Flow Horiz. Horiz. 0.90 0.20 0.05 Still air (both indoors and outdoors) 9.26 5.17 4.32 6.13 2.10 1.25 9.09 5.00 4.15 Up ↑ Down h, W/m².K* Surface Emittance, e 45° slope Up ↑ 45° slope Down 7.50 3.41 2.56 Vertical Horiz. →8.29 4.20 3.35 Moving air (any position, any direction) Winter condition (winds at 15 mph or 24 km/h) Summer condition (winds at 7.5 mph. or 12 km/h) 34.0 22.7