Publisher Summary The accurate calculation of heating and cooling loads is essential to provide a sound bridge between fundamental building design decisions and an operating building. If loads are substantially underestimated, occupants and users will likely be hot or cold. If loads are substantially overestimated, equipment will be oversized (usually wasting money, reducing efficiency, increasing energy consumption, and often imperiling comfort). Accurate load calculations are an important part of the design process. This chapter discusses load calculations. Loads are sensible (affecting air temperature) or latent (affecting relative humidity), or a combination of sensible and latent. Loads may be external (passing through the building envelope) or internal (originating within the building envelope). Equipment and systems are sized from “design” loads, which are calculated using statistically significant weather conditions that reflect a building location's climate. A design-heating load represents heat loss from a building under a series of generally agreed upon assumptions. A designcooling load represents heat flow into a building via the building envelope and from internal sources, again under a commonly accepted set of assumptions. This chapter provides definitions for different types of loads. In addition, the study discusses internal and external loads providing their types and details.