Glossary · Testing & air leaks
Duct leakage to outside
Also called: leakage to outside · duct leakage to outdoors · leakage to outdoors
The part of duct leakage that escapes outside the heated and cooled space, into attics, crawlspaces, garages or outdoors.
What it means
To isolate it, the tester runs a blower door to bring the house to the same 25 pascals as the ducts, so leaks into the living space stop counting. What's left is heated or cooled air being dumped where it does no good. Ducts entirely inside the conditioned space have little leakage to outside even when they leak.
Why it matters in an audit
This is the duct leakage that directly wastes energy, so it's the better number for judging whether duct sealing will pay off.
Typical numbers
Reference values with their sources. Your energy advisor’s report gives the figure for your own house.
| What | Value | Source |
|---|---|---|
| Test setup | House and ducts both held at 25 Pa (within ±0.5 Pa of each other) | basc.pnnl.gov ↗ |