Myth #12 - The guy with the CO tester must be right.  (Way Wrong!)

This is my favorite myth. 

There's nothing more impressive than a technician who pulls out and turns on a CO detector in someone's home.  The technician then proceeds to explain to the customer that the low levels of CO being picked up by his test equipment are "probably" being caused by that old furnace in the basement.

It's enough to make me laugh out loud.

I've only been a party to this kind of super-slueth twice, and I had fun both times.  But, it does make me wonder how many times a year this happens to consumers and how many households have changed out equipment based on this kind of recommendation.

First, anyone who turns on their CO detector inside the structure they're going to test, doesn't know how to use the equipment.

Second, if you check the calibration sticker on the CO meter and it's over 12 months old, forget it.  Reliable readings require a recently calibrated CO detector.  All detector manufacturers require yearly calibration at a test equipment laboratory or their premises.

Third, ask the technician when the sensor in the CO detector was replaced.  If he says the unit is new, ask him to verify the exact age.  Manufacturers usually require sensor replacement every 12 months.  There are two manufacturers that specify a 24 month period, one has a 48 month sensor, but most require yearly replacement.

Fourth, ask the technician how he calibrated the detector he's using.  Calibration kits cost more than some of the cheap CO test meters, but they are vital.  They "prove" that the CO meter is reading CO and displaying the proper reading.  The calibration kit should be used at least once a month, or better yet, each time the CO meter is deployed.

All CO detectors and meters use some sort of electro-chemical sensors.  These sensors have a limited operating life and limited storage life.  They are also subject to fouling or contamination, and can become cross-sensitive to other gasses like CO2, butane, methane, NO2, aerosols and a host of others.

Some sensors may take three or four hours to "clear" once they've been introduced to high levels of CO or other gasses.  Other sensors will clear almost immediately.  In a CO meter, this appears as a very sluggish response to changes in the gasses being picked up.  For example, the CO meter is taken outside, but the CO reading doesn't change for a half-hour or more.  (It would be very unusual for a home with gas appliances to have exactly the same CO reading as the background CO measured outside.)

Just because the technician has a meter doesn't mean they know how to measure CO.