The definition of an ERV unit is a mechanical ventilation system that provides both fresh air and exhaust air. It works by exchanging stale indoor air with fresh outdoor air, while also recovering energy from the exhaust air. This helps to reduce energy costs and improve air quality. ERV units are typically installed in commercial buildings, such as office buildings, schools, and hospitals, but they can also be used in residential homes. ERV units are designed to provide a balanced air exchange rate, meaning that the amount of fresh air being brought in is equal to the amount of exhaust air being expelled. This helps to maintain a comfortable indoor environment and reduce the amount of energy used to heat and cool the space. Additionally, ERV units can help to reduce indoor air pollutants, such as dust, pollen, and allergens, making them a great choice for those with allergies or asthma.