| Electric Data Heat Loss Factors and Graphs Continued Helpful Hint: The graphs for losses from uninsulated and insulated surfaces are hard to read at low temperatures close to ambient. Here are two easy-to-use calculations that are only rule-of-thumb approximations when used within the limits noted. Rule #1: Losses from an uninsulated surface (with an emissivity close to 1.0): (This applies only to temperatures between ambient and about 250°F) Losses (W/in2) = AT (°F) rise above ambient 200 Rule #2: Losses from an insulated surface: (This insulation is assumed to be one inch thick and have a K-value of about 0.5 Btu-in/hr - ft2-°F. Use only for surfaces less than 800°F.) Losses (W/in2) = AT (°F) rise above ambient 950 |