Exfiltration
Exfiltration is the unintentional leakage of indoor air out of a building through gaps, cracks, and openings in the envelope. This loss of conditioned air reduces HVAC efficiency, increases energy use, and can introduce moisture into wall assemblies. Reducing exfiltration improves comfort, indoor air quality, and overall building performance.
💡 Key Takeaways
- ✓Exfiltration is the unintentional leakage of indoor air out of a building through gaps, cracks, and openings in the envelope. This loss of conditioned air reduces HVAC efficiency, increases energy use, and can introduce moisture into wall assemblies. Reducing exfiltration improves comfort, indoor air quality, and overall building performance.
- ✓Exfiltration can drive moisture into walls, increasing mold risk.
- ✓Air sealing should be balanced with proper ventilation.
- ✓Leak reduction lowers HVAC runtime and energy costs.
Exfiltration
/ˌeksˈfɪltrəˌʃən/
Definition
Exfiltration is the unintentional leakage of indoor air out of a building through gaps, cracks, and openings in the envelope. This loss of conditioned air reduces HVAC efficiency, increases energy use, and can introduce moisture into wall assemblies. Reducing exfiltration improves comfort, indoor air quality, and overall building performance.
What is exfiltration in HVAC?
It’s conditioned indoor air leaking out of a building, which increases HVAC load and energy use.
Source: The Cooling Company
Quick Facts
How Exfiltration Works
Air sealing reduces leaks and HVAC load.
Real-World Application
A homeowner seals window gaps and attic penetrations after a blower door test, reducing drafts and lowering heating and cooling bills.
Pro Tip
Use a blower door test to locate leaks, then prioritize sealing at attic penetrations, rim joists, and around windows.
“Use a blower door test to locate leaks, then prioritize sealing at attic penetrations, rim joists, and around windows.”
Important Things to Keep in Mind
- Exfiltration can drive moisture into walls, increasing mold risk.
- Air sealing should be balanced with proper ventilation.
- Leak reduction lowers HVAC runtime and energy costs.
Did You Know?
Modern building codes increasingly require airtightness testing to limit exfiltration.
FAQ
What’s the difference between infiltration and exfiltration?
Infiltration is outdoor air leaking in; exfiltration is indoor air leaking out.
Can exfiltration cause moisture problems?
Yes. Warm, moist indoor air can condense inside walls and cause mold.
Should I seal my home completely?
No. Air sealing should be paired with proper ventilation for healthy air.
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