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Combustion efficiency health — Part 2

June 1, 2011
Many appliance manufacturers and re-badgers are under the impression that natural gas energy content is fairly consistent in the field, and they will do a test firing at the factory with 1,050 BTUs per cubic foot of natural gas.

Many appliance manufacturers and re-badgers are under the impression that natural gas energy content is fairly consistent in the field, and they will do a test firing at the factory with 1,050 BTUs per cubic foot of natural gas. Once they have dialed in this number, they put a dab of witness paint on any adjustment screws, and I've actually seen some manufacturers that will place an adhesive seal over the top of critical air/fuel adjustment screws.

Now understand the chain of control as it pertains to these devices. If improperly adjusted in the field, the units may generate dangerous carbon monoxide levels. Granted, most of the high-efficiency appliances being set in the field are sealed combustion, and the possibility of that CO creating a dangerous condition are much less than the atmospheric equivalent, but it still represents a significant health hazard potential that must be controlled.

Unfortunately, the actual BTU content per cubic foot is not a constant in the field. For example, here in Denver, the utility purveyor intentionally de-rates the BTU content of the natural gas to compensate for the possibility of someone dragging a natural gas fired appliance up to this altitude from a sea level location. Without performing a critical orifice change to compensate for the difference in energy content and atmospheric density differentials, the appliance could spew a significant amount of the deadly CO gas out its vent. The intentional de-ration of the gas is the utility companies' effort to limit their liability due to a misapplication by the consumer. The problem is that most manufacturers assume that our gas at this altitude is full energy content, and in reality, it is not. It is also difficult for the manufacturers to simulate the differences in altitudinal atmospheric density, and it is virtually impossible to know for sure where these appliances will eventually be installed, and here in Colorado, there is a window of opportunity that goes from 3,000-ft. above sea level to as high as 12,000-ft. above sea level.

The common response from the manufacturers is that the negative pressure gas valve is driven by the density and volume of the atmosphere being drawn through the venturi of their intake/gas valve assembly, and that it automatically adjusts for the difference in altitude. Sounds good, as long as the actual energy content is 1,050 BTUs per cubic foot. If it is less than that, then you can expect some minor issues in the field as it pertains to the appliances combustion health.

If you are not performing a combustion analysis, you'd never see these issues, and would assume that the appliance is in good shape. Once the appliance has been tested, commissioned and adjusted, a permanent record should be made with a copy left with the appliance for future reference, and a copy, either digital if possible or hard copy instead, should be kept at a remote site for future reference. This record keeping is critical if you are ever called in to defend yourself. Without this record of proof, you will be throwing yourself onto the mercy of the court system, because in the eyes of the court, if it is not in writing, then no record actually exists. At that point, you have not followed industry recommended protocol, and an accepted "standard of care." The chances of you surviving a test by the legal system becomes much less at that point.

At a recent hydronics seminar that I was teaching at, I asked the room full of contractors how many of them actually owned a digital combustion analyzer. Of the attendees who responded, less than 10% of those in attendance actually owned an analyzer. I took this informal survey one step further. I asked how many of the affirmative contractors understood the information that they were seeing from their analyzers, and less than a quarter of those who answered the original question said they understood the numbers that their analyzers were producing. As a last question, I asked those who had responded negatively, if they paid more attention to the percentage of efficiency number than the air free CO number, and the majority raised their hand.

I then broke the bad news to them, that in most cases of high-efficiency appliances, that percent efficiency number is the least reliable number, and if it was at all possible to block that number out of their analyzer, that they should do so, because there is no less than a 1,000 different ways to get to that number.

To recap, owning an analyzer is only part of the job. Understanding the output numbers and their interpretation is critical, and knowing what to do to change those numbers and bring them into compliance with the manufacturers' requirements. And by all means, don't forget to document your findings two times: one for the jobsite, and one for your permanent records.

Tune in next month as we look at the actual readings obtained in the field, and what actions were taken to influence those readings. Until then, happy tourist season hydronicing!

All Mark Eatherton material on this website is protected by Copyright 2011. Any reuse of this material (print or electronic) must first have the expressed written permission of Mark Eatherton and CONTRACTOR Magazine. Please contact via email at: [email protected].

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