CSLB C-20 HVAC ContractorControls, Electrical and SafetyEasy
A homeowner complains of headaches and dizziness that improve when they leave the house. A technician suspects low-level carbon monoxide exposure from a furnace. What is the most likely underlying cause the technician should investigate first?
- AOversized supply ductwork causing air noise
- BLow refrigerant charge in the cooling system
- CA thermostat set too high causing excessive cycling
- DIncomplete combustion or a cracked heat exchanger allowing flue gas into the return air
Show answer & explanationAnswer & explanation
Correct answer: D. Incomplete combustion or a cracked heat exchanger allowing flue gas into the return air
Chronic mild CO symptoms that resolve when leaving the structure strongly suggest CO is entering the living space, typically from incomplete combustion or a cracked heat exchanger drawing flue gas into the return airstream. Ductwork noise, thermostat cycling, and refrigerant charge have no relation to CO production.
Why the other options are wrong
- A. Duct noise is an airflow issue, unrelated to combustion byproducts.
- B. Refrigerant issues affect cooling, not combustion gas production.
- C. Cycling frequency doesn't generate carbon monoxide.
CO Poisoning Symptoms
Headache, dizziness, and nausea that improve when leaving a building are classic signs of carbon monoxide exposure from a malfunctioning combustion appliance.
- Symptoms improve away from the source
- Cracked heat exchangers are a common cause
- CO is colorless and odorless
- Always test combustion appliances after symptom reports
Memory trick: Symptoms fade when you leave? Blame the flame (combustion).