Published: Jan 1987
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ASTM hot box tests have traditionally been specified for the determination of thermal performance of reflective insulations designed for building applications. These methods require that specimens be representative of the construction to be investigated; however, ASTM committees have yet to standardize the details of specimen mounting. In building applications, multilayer reflective insulations are almost always mounted between framing members (joists or studs), and it is logical to duplicate this construction in hot box evaluations. A variant procedure followed under California regulations allows the nailing flanges of adjacent insulation pieces to be fastened together to form a blanket large enough to stretch across the hot box with no framing members in the test area.
This paper presents a comparison of hot box data showing that such tests, where no framing members are present, can result in the overstatement of R values by as much as nearly 70%, in comparison with data from specimens mounted in the normal manner between framing members, even though the thermal resistance of the framing members has been calculated out. Thus, it appears that significant lateral heat transfer occurs between the insulation and the framing members, and, therefore, the total system must be tested if the results are to be realistic.
reflective insulation, multilayer insulation, thermal insulation, thermal resistance, R, value, thermal conductance, thermal performance, guarded hot box