Wednesday, January 9, 2013

How to Use, and Misuse a Combustion Analyzer.

The picture is an example of what these look like. I use one to diagnose a myriad of furnace issues. With one of these, you can find the efficiency, determine whether a heat exchanger is plugged or leaking and a host of other issues. One common use is to determine whether or not a heat exchanger needs replacement. As a hard, fast rule, 100 parts per million or less carbon monoxide in the combustion gas is acceptable. 100 to 300 indicates a combustion or venting problem, while 1000+ indicates a heat exchanger problem. Either there's a hole, or it's plugged. Most of the time, if it's over 2500 ppm, the heat exhanger is plugged. The problem is that you have to look before condemning the part. If you get a high reading an say it's bad without looking at it, you're doing yourself and your customer a disservice.

As with all repairs on Heating, Ventilation and Air Conditioning systems, please consult a competent professional when in any doubt. Improper repairs can result in serious personal injury, death and property damage. This post assumes the reader has proper training and experience in HVAC service and not a homeowner. All situations are different and this author has no control over the quality and accuracy of your work. All situations are hypothetical and may not apply to yours. Diagnose and effect this and any repairs at your own risk.

A case in point are the Amana 90% efficient furnaces made in late 1980's and 1990's. These have a high failure rate with the plate next to the tubes being a usual culprit. This requires replacing the furnace as a heat exchanger is not available. This means the customer has to spend money to replace the furnace, and while Amana may give the customer an allowance to replace it, they won't honor anything if the heat exchanger itself isn't bad. These have a collector box on the uppermost part of the exchanger, next to the vent. These frequently rot out to the point there are hole visible and will mimic the above. The repair on this is less than $500 as opposed to $3000 or more on labor and code compliance even if the manufacturer buys the equipment. If the box has failed and the rest of it isn't rusted or perforated, you have the option of repairing the furnace over replacement. From experience, the customer appreciates this consideration and the risk of a voided warranty claim is made non existent.

The lesson is to never rely on one means of diagnosis on a major HVAC repair or replacement, unless there is visual proof. Even then, all the facts need to be in order to correctly and thoroughly diagnose an ultimate problem.

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