A technician performs a Title 24 duct leakage test using a duct blaster. Before pressurizing the duct system to 25 Pascals, the technician seals all supply and return registers with tape. What does this test procedure measure?
- AStatic pressure drop across the air handler
- BDesign airflow at each individual register
- CTotal duct leakage (leakage to both inside and outside conditioned space)
- DLeakage to outside only, using the pressure-pan method
Show answer & explanationAnswer & explanation
Correct answer: C. Total duct leakage (leakage to both inside and outside conditioned space)
Sealing all registers isolates the duct system entirely, so the duct blaster fan flow needed to reach 25 Pa measures all leakage from the ducts, whether it leaks into conditioned space or outside — this is the 'Total Leakage' test. The 'Leakage to Outside' test instead uses a blower door in conjunction with the duct blaster and does NOT seal the registers, canceling out leaks to the inside.
Why the other options are wrong
- A. Static pressure drop is measured with a manometer at the air handler, unrelated to duct blaster testing.
- B. Register airflow is measured with a flow hood, not a duct blaster pressurization test.
- D. The leakage-to-outside test requires a simultaneous blower door and unsealed registers, not this setup.
Total Leakage vs Leakage to Outside
Total Leakage testing seals all registers and measures all duct leaks; Leakage to Outside testing leaves registers open and uses a blower door to isolate only leaks that escape the building envelope.
- Total leakage test: registers sealed, duct blaster only
- Leakage to outside test: registers open, blower door + duct blaster together
- Title 24 compliance often requires leakage to outside ≤ 6% of fan flow
Memory trick: 'Sealed registers seal in ALL the leaks — total test.'