Which is a major route of heat loss in a building?

• A. Through air leakage
• B. Through large surface areas with low R-value
• C. Through wind-driven infiltration
• D. Through interior moisture loss

Answer: (A)

Air leakage is the main way heat escapes a building. Warm indoor air finds ways to get out through cracks, gaps around doors and windows, penetrations, and other openings. As outdoor air replaces it, heat is carried away by air movement (convection), which is very effective at transferring energy. Even with good insulation, these leaks bypass the insulation and dramatically reduce overall thermal performance. Wind and pressure differences make these leaks worse, a phenomenon known as wind-driven infiltration, so sealing and creating a continuous air barrier around the building envelope is one of the most impactful ways to reduce heat loss.

Heat loss through large surface areas with low R-value contributes to conduction, but it generally doesn’t match the energy lost through uncontrolled air movement unless those areas are also leaky. Interior moisture loss isn’t a heat transfer path.