In the United States, intercity long-haul trucks idle approximately 1,800 hrs annually for sleeper cab hotel loads, consuming 838 million gallons of diesel fuel per year. The objective of the CoolCab project is to work closely with industry to design efficient thermal management systems for long-haul trucks that keep the cab comfortable with minimized engine idling. Truck engine idling isprimarily done to heat or cool the cab/sleeper, keep the fuel warm in cold weather, and keep the engine warm for cold temperature startup. Reducing the thermal load on the cab/sleeper will decrease air conditioning system requirements, improve efficiency, and help reduce fuel use. CoolCalc is an easy-to-use, simplified, physics-based HVAC load estimation tool that requires no meshing, hasflexible geometry, excludes unnecessary detail, and is less time-intensive than more detailed computer-aided engineering modeling approaches. It is intended for rapid trade-off studies, technology impact estimation, and preliminary HVAC sizing design and to complement more detailed and expensive CAE tools by exploring and identifying regions of interest in the design space. This paper describesthe CoolCalc tool, provides outdoor long-haul truck thermal testing results, shows validation using these test results, and discusses future applications of the tool.