Document omaQ5qeNgXYyMOorZk3yGYJar

American Society of Heating and Ventilating Engineers Guide, 1930 and cannot change the internal resistance to heat flow inherent in the insulation itself. The maximum increase in loss due to air velocity ranges from about 30 per cent in the case of 1 in. thick insulation, to about Chapter 24--Insulation for Pipes and Surfaces (L. B. McMillan. Iron and Sled Engineer, July 1926.) Fig. 8. Heat Losses from Surfaces Exposed to Various Air Velocities 10 per cent in the case of 3 in. thick insulation, provided that.the insula tion is thoroughly sealed so that air can flow only over the surface. If the conditions are such that the air may circulate through cracks and Crevices in the insulation, the increases may be far greater than those, given above. Therefore, it is essential that insulation be sealed as tightly as possible. ' Pipe insulation out-of-doors should be provided with a weather-proof jacket, and other outdoor insulation should be thoroughly weather-proofed. 414 Fig. 9. Chart for Determining Economical Thickness of Insulation 415