Should You Run an ERV During Summer Humidity? – GreenBuildingAdvisor

By Chuck Bickford | July 14, 2025

Because the envelope of a modern, energy-efficient house is constructed to limit air exchange with the outside, —in other words, “built tight”—, a mechanical ventilation system of some type is recommended. Whether heating or cooling, a home needs a regular supply of fresh air to maintain good indoor air quality. Of course, you could open a window, but depending on the season, the money you just spent on heating or cooling might literally be going out that window. A modern ventilation strategy to provide fresh air and reduce energy waste is called an Energy Recovery Ventilator or ERV. The beauty of this system is the ability to transfer both heat and moisture between the fresh and exhaust air streams, all while maintaining a balanced house pressure.

“EliciaD” —let’s just call her Elicia—recently posted a question on the Q&A forum. Elicia states that she has a modern energy-efficient house in the humid South. The house uses a mini-split system to provide space conditioning and an ERV to provide balanced recovery ventilation. She writes that the mini split isn’t dehumidifying adequately, “even with all the doors and windows closed and ERV not running, but I still need fresh air.” She has questions: