Energy healing ventilators (ERVs) improve indoor air quality by exchanging stagnant indoor air with fresh outdoor air

https://blogfreely.net/neasalnrfx/air-purifier-change-filter-light-wont-switch-off-solutions-here

Energy healing ventilators (ERVs) enhance indoor air quality by exchanging stale indoor air with fresh outside air while retaining heat or coolness as needed.