From reading the discussions of "rightsizing" in the "green building" literature, one would infer that most HVAC engineers have large holdings in HVAC equipment manufacturer stock. Many of these texts, often intended for architects, warn their readers to be on the lookout for maliciously oversized HVAC equipment, stating explicitly that large first cost and energy cost savings can be accrued from detecting and correcting this mischief. While oversizing of HVAC equipment may occur, it is rarely with intent to line the pockets of vendors; rather, it is usually the result of efforts to protect both the engineer and owner from inadequate capacity. Understanding the actual uncertainties of load calculations and providing systems that can function effectively and efficiently at part loads will help both the engineer and the building owner avoid the unpleasantness of an undersized conditioning system.