A problem on the steady flow of heat through glass is treated mathematically. It is shown that though infrared energy is absorbed within a short distance by almost any glass, the reradiation of energy by the glass itself is sufficient at glass-melting temperatures to cause a considerable flow of heat. At 1200°C the radiant heat flow within a common window glass is of the order of fifty times the ordinary conductive flow. The effect is much less important at lower temperatures because the total radiant energy is smaller and because most glasses are very opaque to the longer infrared wavelengths involved.
B. S. KELLETT, "The Steady Flow of Heat through Hot Glass," J. Opt. Soc. Am. 42, 339-342 (1952)