Example. How much calcium silicate insulation is required on a 650°F duct in an 80°F ambient temperature if the maximum heat loss is 50 Btu/hr ft2? The insulation will be finished with a mastic coating.

STEP 1. Assume that ts = 105°F. So tm = (650 + 105)/2 = 377°F. k from Table 15-1 or appendix Figure 15.A1 at 377°F = 0.46.

STEP 2. Find tk as follows:

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