The definition of a HVAC ERV (Energy Recovery Ventilator) is a system that is designed to improve the indoor air quality of a home or commercial building by exchanging stale air with fresh air from outside. It works by transferring heat and moisture from the outgoing air to the incoming air, while still providing adequate ventilation. This helps to reduce energy costs, as the incoming air is pre-conditioned and does not require additional heating or cooling. Additionally, it helps to reduce indoor air pollutants, as the air is constantly being filtered and exchanged. HVAC ERV systems are becoming increasingly popular in homes and businesses due to their energy efficiency and air quality benefits.