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These 10 free Combustion Analysis questions are organized by exam domain, so you can see how each part of the Combustion Analysis Certification blueprint is tested. Reveal the answer and explanation under each question.
An oil burner has elevated CO despite verified fuel input, a leak-free flue sample, and appreciable residual oxygen. Its flame contacts a relatively cold chamber surface. Which additional finding would most strongly support temperature quenching as a contributor?
Correct answer: B - CO falls after an approved correction removes the contact, with input and flue O₂ unchanged.
A furnace at high fire and a water heater are the only gas appliances firing during an input check, and both remain steady. Together they consume 3.0 ft³ in 90 seconds; the utility heating value is 1,025 Btu/ft³, with no meter correction needed. The water heater's independently verified input is 41,000 Btu/h. The furnace manufacturer permits 76,000-84,000 Btu/h at high fire. What does the meter test establish about the furnace?
Correct answer: B - 82,000 Btu/h; the furnace's fuel-input requirement is met.
A CO alarm is sounding when a technician arrives at a house. One resident has a headache and appears confused. Another has opened several windows, and the technician's functioning ambient monitor now reads 6 ppm. What takes priority?
Correct answer: C - Move everyone outside and call emergency services from outside.
A manometer displays INPUT pressure minus REF pressure. INPUT is exposed to the combustion appliance zone, and REF is connected outdoors. The baseline is +0.8 Pa; with the selected exhaust equipment operating, the reading is −4.7 Pa. Automatic baseline correction is off. The exhaust-induced pressure change should be recorded as:
Correct answer: A - −5.5 Pa: additional depressurization relative to outdoors.
A technician tries to measure duct static pressure with a plain, open-ended tube. The reading is higher with the opening facing upstream and lower when the tube is rotated, although blower operation remains steady. Before interpreting the duct pressure, the technician should:
Correct answer: B - Fit a proper static-pressure pickup and repeat the measurement.
Supply and return ducts pass through a mechanical closet, with no grille opening into it. With burners and exhaust fans off, starting the circulation blower makes the closed closet negative relative to the hallway. Hallway pressure relative to outdoors does not change. Opening the closet door largely removes the difference. Identify the defect most consistent with this pattern.
Correct answer: D - Return-duct leakage extracting air from the closet.
Two analyzers sample the same natural-gas appliance at steady operation. Both measure O₂ and CO, but neither has a CO₂ sensor. Their O₂ readings agree at 5.0%, while their displayed CO₂ values differ substantially. Before treating this as a disagreement between gas sensors, reconcile the analyzers'-
Correct answer: A - selected fuels used to calculate CO₂ from measured oxygen.
A steady burner is left unchanged while the analyzer's condensate trap is emptied. After reconnection at the same approved sampling port, O₂ rises from 5.2% to 13.8% and raw CO falls from 110 ppm to 50 ppm. Flue temperature changes by less than 2°F. Both gas readings settle at their new values. Where should troubleshooting begin?
Correct answer: D - At the trap seals and hose connections, checking for sample-air leakage.
Following Beckett's 2017 flame-retention-burner adjustment procedure, a technician reaches steady operation and establishes trace smoke using a 10-stroke sample. Increasing air lowers CO₂ by 1.5 percentage points. A second properly taken smoke sample still shows a slight stain, although the other required readings are acceptable. Has the adjustment reached the procedure's intended endpoint?
Correct answer: D - No; the final setting must also produce a zero-smoke test.
A pregnant resident developed headache and nausea while a fuel-burning heater operated. She is now outside awaiting emergency assistance, and her symptoms have eased. A conventional two-wavelength fingertip pulse oximeter displays a stable SpO₂ of 98%. Which interpretation can the technician responsibly give?
Correct answer: C - Conventional pulse oximetry is unreliable with carboxyhemoglobin; this reading cannot exclude CO poisoning.
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