Exfiltration
Definition and meaning of Exfiltration in real estate.
Exfiltration is the uncontrolled leakage of indoor air out of a building through cracks and gaps in the structure's envelope. This escape of conditioned air is caused by pressure differences between the interior and exterior environments.
In more detail
While ventilation is the deliberate exchange of air, exfiltration is accidental and leads to significant energy loss. As warm, conditioned air leaks out of the upper levels of a home, cold outdoor air is drawn in through lower levels to replace it, a phenomenon known as the stack effect.
Common pathways for exfiltration include gaps around windows, doors, attic hatches, and plumbing penetrations. Sealing these gaps improves energy efficiency, lowers utility bills, and helps maintain consistent indoor temperatures. Home buyers often request a blower door test during a home inspection to identify these leakage areas.
Key facts
| Category | Property Types & Construction |
|---|---|
| Common cause | Temperature and pressure differences between the inside and outside of a home |
| Typical remedy | Applying caulk, weatherstripping, and expanding foam insulation |
| Detection method | A professional energy audit utilizing a blower door test and thermal imaging |
During a cold winter, warm heated air escapes from a house through cracks around the attic hatch, causing the furnace to run more frequently and raising the heating bill.
Frequently asked questions
What is the difference between exfiltration and infiltration?
Exfiltration is indoor air leaking out of a building, whereas infiltration is outdoor air leaking into a building through the structural envelope.
Why is excessive exfiltration bad for a home?
It wastes energy, increases utility bills, makes indoor drafts common, and can allow moisture to escape into wall cavities where it can cause mold.