The guarded hot box is a test apparatus that measures the thermal conductivity of full-size walls. While energy-efficient walls can be built with dimensional lumber, it takes careful design and construction to achieve this. Building owners, builders, contractors, and designers interested in constructing energy-efficient homes may wish to consider using alternative wall materials, whether for their potential energy savings or for a host of other reasons. These reasons may include thermal comfort, lower cost, fire safety, hurricane resistance and enhanced protection from other natural disasters, durability, noise reduction, architectural flexibility, and use of recycled or reused materials. In the predesign stage, when homeowners or builders are weighing the relative merits of alternative wall systems, they must be able to accurately compare the R-values of those systems.
Thermal shorts result in unwanted heat loss in the winter and heat gain in the summer.
However, it is much more difficult to estimate the thermal performance of other wall systems accurately, particularly if several different system types are being considered at the building conceptual design stages. Now the thermal performance of alternative wall systems can be compared fairly easily by anyone who has Internet access. More than 15 wall system manufacturers submitted 40 different wall systems for the hot-box tests. These tests generally validated the results from thermal modeling we also conducted, but occasionally generated unexpected findings. Computational fluid dynamic modeling revealed that this lower R-value resulted from internal convection in the discontinuous gaps between the stucco and the straw bales and between the drywall and the straw bales.