A survey questionnaire dealing with instrumentation, calibration and error estimation of guarded and calibrated hot boxes was mailed to United States and Canada hot box laboratories capable of measuring the R-value of building assemblies. Questions pertaining to types of instrumentation, estimated accuracy of the specific instruments and error analysis calculations were asked. Responses from those laboratories responding to the survey are summarized in the paper. This information will be beneficial to future revisions of the ASTM guarded and calibrated hot box test methods.