[en] The Yucca Mountain Project conducted a Single Heater Test (SHT) in the Exploratory Studies Facility at Yucca Mountain. During the nine month-long heating phase, approximately 4 m³ of in situ, fractured, 92% saturated, welded tuff was heated to temperatures above 100 C by a 5 m long, 3.8 kW, horizontal, line heater. In this paper, the thermal data collected during the test (Sandia National Laboratories, 1997) are compared to three numerical simulations (Sobolik et al., 1996) in order to gain insight into the coupled thermal-hydrologic processes. All three numerical simulations rely on the Equivalent Continuum Model (ECM) for reasons of computational efficiency. The ECM assumes that the matrix and the fractures are in thermodynamic equilibrium which allows the thermal and hydrologic properties of the matrix and the fractures to be combined into single, bulk values. The three numerical simulations differ only in their bulk permeabilities and are referred to as the High, Low and Matrix Permeability Models, respectively. In the Matrix Permeability Model, the system behaves as an unfractured porous medium with the properties of the rock matrix