CSLB C-20 HVAC ContractorVentilation and Air DistributionHard
A technician performs a combustion appliance zone (CAZ) worst-case depressurization test with all exhaust fans and the air handler running. The CAZ depressurizes to -5 Pa relative to outdoors, while the manufacturer's spillage-safe limit for the atmospherically vented water heater is -3 Pa. What should the technician do?
- AFail the test and take corrective action, such as providing makeup air, before returning the appliance to service
- BPass the test since -5 Pa still indicates negative pressure, which is expected
- CIncrease exhaust fan CFM further to confirm the spillage risk before making a decision
- DIgnore the result since atmospherically vented water heaters are not affected by house depressurization
Show answer & explanationAnswer & explanation
Correct answer: A. Fail the test and take corrective action, such as providing makeup air, before returning the appliance to service
Because the measured depressurization (-5 Pa) exceeds the manufacturer's safe limit (-3 Pa), the appliance is at risk of backdrafting or spillage of combustion gases. The technician must fail the test and correct the depressurization, typically by adding makeup air or reducing exhaust loads, before the appliance can be safely returned to service.
Why the other options are wrong
- B. Exceeding the safe limit is a fail condition, not an acceptable pass.
- C. Increasing exhaust further would worsen the hazard and endanger occupants.
- D. Atmospherically vented appliances are highly susceptible to depressurization-induced spillage.
CAZ Worst-Case Depressurization Test
A safety test that measures pressure in the combustion appliance zone under worst-case exhaust conditions, compared against manufacturer spillage limits for atmospherically vented appliances.
- Typical safe limit for atmospheric appliances is around -3 to -5 Pa depending on manufacturer/testing protocol.
- Exceeding the limit indicates backdraft/spillage risk of carbon monoxide.
- Corrective actions include makeup air, reducing exhaust CFM, or appliance venting changes.
Memory trick: Too much suck, appliance backdraft luck runs out.