Newer, "weather tight" homes tend to increase the risk of CO poisoning due to the potential for negative pressure and insufficient combustion air supply, and retention of spilled exhaust gases inside.
The protocol for CO sampling and evaluation can vary by structure, region, etc. However, there are certain basic steps that should be followed to achieve comprehensive and reliable test results.
CO Testing Outline: Sample
A CO analyzer with draft (or a separate draft gauge), and a combustible gas leak detector are a must.
Outside air should be sampled for CO, and external gas appliances checked for gas leaks. Potential sources of outside CO contamination include traffic, garages, industry, and combustion exhaust from adjacent structures.
The first indoor air sample should be taken at the front door threshold. All rooms within or attached to the living space should be tested for CO and gas leaks. Inside CO levels should be equal to or less than outside, but in no case greater than 9 ppm. Any dangerous levels should prompt immediate evacuation.
After confirming that the environment is currently safe, all combustion appliances and exhaust fans should be turned off, all exterior doors and windows closed, and all interior doors open (pilots remain lit). An ambient CO sample should be taken in the main living space.
The furnace(s) should be turned on for at least five minutes. The main living space should be tested again, as well as the atmosphere just above heat exchanger or in supply register nearest furnace. These latter levels should be the same, and not exceed 9 ppm of CO.
All of the remaining combustion appliances should be turned on and tested for CO and draft. Exhaust fans should be operating (except whole house fans). If CO is measured at vent termination, then combustion appliances sharing a common vent should be tested individually. Tests should be conducted with both the appliance closet door(s) closed, and again with one door open. Filters must be clean and in place.
Sample locations include furnace flue or vent pipe termination, water heater diverter, cooktop burners, oven exhaust termination, and gas dryer moisture exhaust outlet. Heat exchangers should be inspected for cracks or defects.
Visual clues of potential CO production include:
This outline is not intended to be complete. Please refer to instructions provided by the combustion appliance and CO analyzer manufacturers.
CO Monitoring Service
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