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[Editor's note: This is part four of a five-part series.]
Before you test any equipment at an existing installation, before you even perform a clean and check or other maintenance, you need to check ambient carbon monoxide (CO) levels before entering the home. Run the equipment through a complete cycle unless you are there for a no-heat call.
If at any time during this test, ambient CO levels exceed 100 ppm, evacuate occupants and ventilate the dwelling immediately. For lower CO levels, consult the "Ambient CO Limits" section of the Testo Combustion Guide or consult a local authority with jurisdiction over these matters.
Perform the test before entering any home, boiler room, basement, or crawlspace where an appliance is located. CO levels in the home should always be verified before you enter the space, and before you zero the analyzer for an appliance combustion test. If you do not use an ambient combustion air temperature probe, the analyzer must be rezeroed when the probe is surrounded by air similar in temperature to the air that is used for combustion if CO is present.
Appliance safety should be the primary goal of all technicians. The amount of CO in flue gases should be kept below 100 ppm air free, even though the allowable limit in the stack is 400 ppm air free.
RISING LEVELS
Whenever CO is rising and not stable at any level from 100 to 400 ppm during the combustion process, the burner should be shutdown and/or immediately repaired. A burner with rising CO is far more dangerous than a stable reading because the CO can continue to rise far above dangerous levels.
Levels above 400 ppm are not permissible and require the immediate repair and/or shutdown of the appliance.
The ambient measurement of CO does normally result from a cracked heat exchanger. More often than anything else, it is the result of auto exhaust from an attached garage, and/or depressurization of the home, resulting in sufficient air for combustion.
If CO is detected, all possible sources should be checked, including, but not limited to, water heaters, gas ovens and stoves, the furnace, nonelectric space heaters, and vented or unvented appliances, like gas logs and fireplaces.
PERFORMING A DRAFT TEST
All appliances are...