CSLB C-20 HVAC ContractorVentilation and Air DistributionMedium
A technician performs a pressure pan test as part of duct leakage diagnostics. With a blower door depressurizing the house to -25 Pa relative to outdoors, the technician seals a pan over a supply register and reads 0.3 Pa on the manometer. What does this low reading most likely indicate?
- AThe register itself is defective and must be replaced
- BThe duct connected to this register has severe leakage and needs immediate sealing
- CThe duct connected to this register is well-connected and has minimal leakage to outside
- DThe blower door fan is undersized for the volume of the house
Show answer & explanationAnswer & explanation
Correct answer: C. The duct connected to this register is well-connected and has minimal leakage to outside
In a pressure pan test, the house is depressurized and a sealed pan isolates the duct at each register, measuring the pressure difference between the duct and house. A reading near 0 Pa means the duct is essentially communicating only with the house interior (tight connection), while readings of several Pascals indicate leakage paths to outside or unconditioned space.
Why the other options are wrong
- A. A defective register would not typically be diagnosed this way.
- B. Severe leakage would produce a much higher pan reading, not near zero.
- D. Blower door sizing affects house depressurization capability, not this individual reading.
Pressure Pan Test
A diagnostic test that measures the pressure differential at each register while the house is depressurized by a blower door, used to locate and quantify duct leakage to outside.
- House is depressurized to a reference pressure (commonly -25 Pa)
- Low pan readings (near 0 Pa) indicate tight ducts
- High pan readings (several Pa) indicate leakage to outside
Memory trick: Low number, tight tunnel — high number, hole in the wall.