Which of the following is an example of a thermal by-pass?

A thermal by-pass refers to a situation where heat flows through an unintended path, often leading to inefficiencies and comfort issues within a building. The correct choice focuses on the concept of how thermal energy can move through structures, particularly in the instances where there are routes that allow conditioned air to bypass its intended path.

In the context of pipe chases, these are vertical or horizontal conduits in a building that contain piping for plumbing, heating, or cooling systems. If not properly sealed and insulated, pipe chases can allow heat to escape or infiltrate areas where it is not needed. This unintentional movement of thermal energy effectively creates a thermal by-pass, as it enables air or heat to travel away from its designed pathway, thus impacting energy efficiency and temperature control within the structure.

The other options, while related to building components and systems, do not exemplify thermal by-passes in the same way. Radiators are designed for focused heat delivery, crossover ducts are meant to facilitate airflow between areas rather than bypassing it, and fireplaces typically serve as controlled heat sources rather than pathways for unintended thermal flow. Understanding the nature of thermal by-passes is crucial for effective insulation and energy efficiency strategies in building design and maintenance.