CSLB C-20 HVAC ContractorHeating SystemsHard
A technician is performing a combustion analysis on a natural gas furnace. The measured CO (carbon monoxide) level in the flue gas is 400 ppm (parts per million) undiluted. What action should the technician take, according to safety protocols and code requirements?
- AShut down the appliance and red tag it as unsafe, then notify the homeowner.
- BAdjust the gas pressure slightly to achieve a lower CO reading.
- CIncrease the primary air to the burner to lean out the flame.
- DInspect the heat exchanger for cracks or failures immediately.
Show answer & explanationAnswer & explanation
Correct answer: A. Shut down the appliance and red tag it as unsafe, then notify the homeowner.
According to most industry standards and safety protocols (e.g., ANSI Z21.1, NFPA 54), undiluted CO levels exceeding 400 ppm are considered immediately dangerous and indicate a severe combustion problem. The appliance must be shut down and tagged as unsafe, and the homeowner notified to prevent potential carbon monoxide poisoning.
Why the other options are wrong
- B. While gas pressure adjustment can impact CO, 400 ppm is too high for a simple adjustment; it indicates a serious underlying issue.
- C. Adjusting primary air can affect CO, but again, 400 ppm is an emergency level requiring immediate shutdown, not just an adjustment.
- D. Inspecting the heat exchanger is a crucial diagnostic step, but the immediate priority with 400 ppm CO is to shut down the appliance for safety, then proceed with diagnosis.
Dangerous CO Levels
Carbon monoxide (CO) levels in flue gas, particularly undiluted, that exceed specific thresholds (e.g., 400 ppm) are considered immediately hazardous and require the appliance to be shut down.
- CO is a colorless, odorless, toxic gas.
- High CO indicates incomplete combustion or flue gas recirculation.
- Industry standards define dangerous levels requiring immediate action.
Memory trick: When CO hits four hundred, safety's call cannot be blundered.