Carbon monoxide (CO) testing detects this colorless, odorless toxic gas produced by incomplete combustion in furnaces, boilers, and water heaters. HVAC technicians use electrochemical CO meters to measure concentration in parts per million (ppm), sampling from flue gases and indoor air. This critical safety test identifies dangerous appliance operation before poisoning occurs.
Testing Standards and Limits
The OSHA 8-hour workplace exposure limit is 50 ppm. ASHRAE standards recommend residential indoor CO levels not exceed 35 ppm averaged over 1 hour. During flue gas analysis, CO above 400 ppm indicates incomplete combustion requiring immediate corrective action. Residential ambient air readings above 10 ppm suggest a combustion appliance problem or external contamination source.
Testing Methodology
Technicians measure flue gas CO at the appliance outlet and indoor ambient air simultaneously. Modern digital CO meters provide readings within 2-5 ppm accuracy and respond within 30-60 seconds. Annual testing during furnace maintenance, after component replacement, or when occupants report symptoms like headaches or nausea provides early warning of hazardous conditions. Residential properties should also install battery-operated or hardwired CO detectors as supplemental protection.