Which of the following is NOT a reason to retest for radon?

Retesting for radon is typically recommended under specific conditions that could potentially impact the levels of radon in a home. Significant alterations to heating, cooling, or ventilation systems can affect air pressure and circulation within the home, which in turn can influence radon levels. Similarly, a new addition increases the home's overall footprint and could alter the dynamics of how radon enters from the soil.

In contrast, the arrival of a new neighbor does not inherently affect the radon levels in your home. Radon is a naturally occurring gas that emanates from the ground, and neighbor activity or changes do not have a direct impact on the physical structures or environmental conditions of another property in terms of radon exposure. Therefore, while it's important to monitor radon levels, moving neighbors is not a valid reason to retest for radon in an existing home.