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Example. For an 850°F boiler operating indoors in an 80°F ambient temperature insulated with 4 in. of calcium silicate covered with 0.016 in. aluminum jacketing, determine the heat loss per square foot of boiler surface and the surface temperature.

STEP 1. Find k for calcium silicate at tm. Assume that ts = 140°F. Then tm = (850 + 140)/2 = 495°F, k at 495°F = 0.53, from Table 15-1 or appendix Figure 15.A1.

STEP 2. Determine Rs for aluminum from Table 15.4. ts - ta = 140 - 0 = 60°F, so Rs = 0.85.

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