What does thermal bypass refer to in a building?

Thermal bypass refers to airflow that carries heat across the thermal boundary of a building. This phenomenon occurs when air flows through gaps, cracks, or poorly insulated areas, which allows warmer air from inside the conditioned space to escape or allows unconditioned air from outside to infiltrate the building. This can significantly compromise a building’s energy efficiency, as it leads to unwanted heat loss in winter and heat gain in summer. Ensuring proper sealing and insulation can minimize thermal bypass, ultimately improving comfort and reducing energy costs.

The other options do not accurately capture the essence of thermal bypass. For instance, heat radiating from windows pertains to heat transfer via radiation rather than airflow. Loss of heat during the summer relates to cooling needs and does not specifically address the concept of bypassing thermal barriers. Heat generated by appliances is an indoor phenomenon not related to the thermal boundary and its management. Thus, the focus on airflow across the thermal boundary makes the first option the correct definition of thermal bypass.