This paper documents ASHRAE Research Project (RP) 1766, Development of a Unified Tool for Analysis of Room Loads and Conditions.The primary result of the project is the Radiant Perfor-mance Explorer/Heat Balance (RPEHB), a PC-based Windows application that derives and displays comfort results for multiple positions within an arbitrarily shaped room. RPEHB draws on and unifies work from several prior ASHRAE research projects. The work involved translation of Loads Toolkit Fortran code to C++and the creation of an integrated application that allows designers to investigate space performance starting with known inputs only. Support for the EnergyPlus IDF file format allows use of graphical tools such as OpenStudio/ Sketchup for input preparation. Key modeling inputs can be modified interactively within RPEHB, including heating and cooling set points, supply air temperatures, panel surface temperatures, solar gain, occupant posture, and comfort parameters (clothing and activity). RPEHB performs design-day heat balance calculations that yield surface temperatures, surface radiant and convec-tive flux, system air loads, and total radiant output. Mean radi-ant temperature (MRT) is calculated for a grid of occupant positions using geometric view factor methods that support arbitrary room shape. This in turn allows derivation of common comfort measures, including predicted mean vote (PMV), predicted percentage dissatisfied (PPD), operative temperature, and radiant temperature asymmetry. RPEHB displays these results in a computer-graphics-based visualiza-tion screen. Generation of comfort result export files is supported. RPEHB can also be used to derive and display comfort conditions with surface temperature results imported from EnergyPlus. A noninteractive batch mode is also supported.