Calibration methods are presented in this paper to convert the response of heat flux transducers (HFTs) to heat flux for the analysis of in-place thermal performance of building envelopes. In general, the heat flow through any boundary of a building envelope can be measured, provided HFTs are properly calibrated. There are at least two measurement alternatives, depending on the placement of HFTs on building envelope subsystems such as walls or roof decks. In one alternative (the embedment technique) HFTs are embedded within the subsystem. In this situation, the proper calibration can be carried out in the laboratory with the HFT embedded in the same construction material. In the other alternative (the attachment technique), HFTs are attached externally, for example, to the inside surface of the subsystem. Thus, the technique is nondestructive. HFTs used in this manner are exposed to the specific building enclosure environment. Therefore, their response is affected by the prevailing convective and radiative conditions, HFT/subsystem surface interaction, subsystem geometry, and, to a lesser extent, subsystem surface temperature. The purpose of this paper is to describe recommended HFT calibration methodologies for the two HFT application techniques and to present some calibration data. The methodologies take into account the important factors that are essential for a complete description of the HFT responses.