Why Tight Homes Need Fresh Air 💨 | Blower Door Test Explained! We’re breaking down what happens when you run a blower door test on homes insulated with foam, fiberglass, or cellulose and why it’s not just about sealing your house tight. When a home is insulated correctly, it becomes so airtight that fresh air can’t naturally circulate which is great for energy savings, but tough on indoor air quality. That’s where mechanical ventilation systems come in. Adding a fresh air intake to your HVAC ke