We’ve been told that opening windows is enough to clean up indoor air. And sometimes, it is. But not for most people, and not without tradeoffs.

Lüften, the practice of opening windows fully for 15 to 30 minutes a day, is widely recommended as a way to bring in fresh air. But in modern buildings and especially for sensitive individuals, it often doesn’t work the way people think it does.

This is the first video in a 4-part series on ventilation strategies that actually work year-round, even for renters. I break down the hidden limitations of Lüften and why I rely on ERVs (energy recovery ventilators) to get truly clean air indoors.

If you’re dealing with biotoxin illnesses like CIRS or MCS, this one’s for you.