Combustion Air Separation and CO in a Packaged Rooftop Unit
During an inspection of a 22,000 sq ft single-story office and warehouse, you access three rooftop packaged gas/electric units. RTU-2, a 2011 10-ton unit serving the office area, shows rust streaks and scorched paint around the burner access panel. A 3 in flexible combustion-air duct has separated from the unit inlet, and stored boxes block the outside-air louver. After ten minutes of operation in heating mode, your CO meter reads 9 ppm in the supply airstream and 0 ppm in the outdoor ambient air. The building is occupied by about 40 office workers. You are not a licensed HVAC technician and have no combustion analyzer. The property manager says the unit "was serviced last month" and asks you not to alarm tenants.
1. What immediate action and notification are appropriate?
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The combination of scorched paint, rust at the burner access, disconnected combustion-air duct, blocked louver, and measurable CO in the supply airstream is enough to treat RTU-2 as a potential combustion-gas entry problem. Recommend shutting the unit down in heating mode until a qualified HVAC contractor inspects the heat exchanger, burners, flue, and combustion-air pathway. Notify the property manager in writing the same day, and recommend that the owner notify tenants if the unit remains in service. A 9 ppm supply-air reading is not by itself an evacuation trigger under common occupational limits, but it is abnormal and should not be dismissed as a meter quirk. Do not attempt repairs, adjust gas pressure, or remove the burner panel. Also do not tell the manager the unit is safe because the reading is low; low-level CO can still indicate a compromised heat exchanger or backdrafting.
2. How should the report characterize the CO reading and the burner condition?
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Report the reading as a spot measurement with stated conditions: heating mode, ten minutes of operation, supply airstream, 9 ppm, with 0 ppm outdoor ambient. State the instrument type and that it was not a combustion analysis. Describe the physical evidence separately: rust streaks, scorched paint, disconnected combustion-air duct, and blocked louver. Then conclude that the observations indicate a potential combustion-gas entry condition and combustion-air deficiency requiring evaluation by a licensed HVAC contractor. Avoid diagnosing a cracked heat exchanger; visual inspection and a spot CO meter cannot confirm that. Also avoid saying the space is safe or unsafe based on one reading. If the report includes a hazard rating, explain the basis: the unit serves occupied office space, combustion air is compromised, and CO was detected in supply air, so the condition merits prompt correction rather than routine maintenance.
3. What should you recommend, and what should you avoid saying?
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Recommend immediate shutdown of RTU-2 in heating mode, repair or replacement of the combustion-air duct, removal of storage blocking the louver, and a full combustion analysis and heat-exchanger inspection by a qualified contractor. Recommend confirming that the other two units have unobstructed combustion air and no similar distress. Recommend the owner retain the contractor's written findings because the unit was reportedly serviced recently. Avoid saying the building has CO poisoning, that the heat exchanger is cracked, or that tenants must evacuate based solely on 9 ppm. Avoid accepting the manager's request to soften the language; instead explain that the report will be factual and that the manager can respond to the findings. Document the conversation and the unit's condition with photographs and readings, and state the limitations of a non-invasive, spot-check inspection.