What type of pressure difference do return leaks create in a house with respect to the outside?

Return leaks in a home’s HVAC system create a negative pressure difference with respect to the outside. When air escapes from the return ducts due to leaks, the system draws in more air from the surrounding areas in an attempt to maintain the desired airflow and pressure balance. This results in lower pressure inside the house compared to the outside environment. Consequently, the home essentially becomes a vacuum, pulling air in through various openings, which can lead to unwanted infiltration of outside air.

The concept of pressure differences is crucial in understanding how air flows through a building's shell and HVAC system. When return leaks occur, the pressure differential created drives unconditioned air into the home, which can compromise comfort levels and energy efficiency. Proper sealing of return ducts and ensuring a balanced HVAC system is essential in achieving optimal performance and maintaining indoor air quality.