Positive pressure vs. negative pressure
I have heard contradictory claims from ventilation specialists and building owners alike.
Sometimes positive pressure is recommended so that “cold air doesn’t enter through cracks,” and other times negative pressure is suggested so that “moisture doesn’t move into the structure.”
So which is correct? From a building physics perspective, the answer in the Estonian climate is clear.
❌ Myth: A building should have slight positive pressure to prevent cold air and dust from entering through leaks.
✅ Reality: Positive pressure pushes warm, moist indoor air through cracks and electrical outlets into the wall structure. When this air meets the cold outdoor environment, condensation forms. The result: wet insulation materials, mold, and rot.
Why do we need slight negative pressure in winter?
Negative pressure draws cooler outdoor air (with lower absolute humidity) through the structures into the building. As this air warms up, its relative humidity decreases, which helps dry the structures.
A simple rule to remember when setting ventilation:
The side with the higher temperature should have lower pressure.
At the equator (where it is hot and humid outside), it makes sense to maintain positive indoor pressure. In our climate (where it is cold outside), it is essential to maintain slight negative indoor pressure.
Protect the health of your house and check whether your ventilation system is operating in the correct mode! 🏠💨🌡️