The educational material analyzes heat loss. Heat loss refers to the transfer of thermal energy from a hotter object to the surroundings or to a cooler object, and it occurs by three mechanisms: conduction, convection, and radiation. Conduction occurs within a body or between two bodies in contact and involves the direct microscopic exchange of kinetic energy of particles through the boundary between two systems. Convection depends on the motion of mass from one region of space to another, and it occurs when bulk flow of a fluid (gas or liquid) carries heat along with the flow of matter in the fluid. Radiation is heat transfer by electromagnetic radiation, such as sunshine, with no need for matter to be present in the space between bodies. There are four types of heat loss in a building, including thermal radiation, conduction, convection, and air infiltration. To reduce heat loss in a building, designers use different techniques, such as adding thermal insulation to the building fabric, reducing air infiltration through cracks and joints, and increasing energy efficiency. To calculate heat loss in a building, one can use the R, K, and U-values of all the external building fabric elements, volume, and average ventilation rate to calculate the overall heat loss coefficient using a formula that considers many variables such as heat transmission, the element’s conductance, ventilation, and thermal resistance. The R-value refers to the material’s resistance to heat flow through the material, while the K value measures the heat flow through an individual substance. The U-value measures the overall building heat loss and is a more complex value.The document also includes some exercises with their solutions, in order to be as much as possible clear for the students.