Is Oxygen Trim Worth the Price?
The amount of oxygen in the flue gas off of a boiler indicates how much excess air is in the flue gas mixture. The lower the amount of excess air is, the higher the boiler efficiency is. In other words, the more efficient your fuel dollars are being spent. Oxygen Trim systems gather the amount of oxygen and then position the air damper to the proper position to maintain a set point. In that way barometric, fuel temperature and other factors don’t force the boiler to run less efficiently than it is capable of being. If the excess air could be cut from 20% to 10% there would be about a 1% reduction in fuel expense. That sounds good but these systems cost a good deal of money and many times they are not capable of yielding the return on investment that was promised or anticipated. How can you tell if an oxygen trim system is a good investment? There are a couple of factors that determine if the answer is “yes” or “no.” Can the burner perform better after the thousands of dollars have been spent? Many burners have mixing heads that are not capable of operating over a wide range of fuel inputs without requiring that a lot of excess air to provide sufficient air and fuel mixing to achieve low and safe carbon monoxide values. If the burner cannot run efficiently (say less than 50 PPM of CO) at low fire then oxygen trim is probably not worthwhile. To determine this, place the burner on low fire. Adjust the air damper so that excess air is decreased to where the level of carbon monoxide is around 50 PPM. Then watch to see if the values are stable. If they are you must ask yourself why they were not set to that point before you started this adventure. Ask the burner technician that set the burner up that way. He may tell you that he noticed higher CO values at that excess air level on the day he set the burner up. If that is the case . . . oxygen trim is probably not a good investment. Most local and National Codes require that at least 15% excess air (3% oxygen) to used unless an oxygen trim system is installed. Therefore note what the O2 value is. If it is not in the 1.5% to 2.0% range then we don’t recommend oxygen trim. If the CO values remain stable AND the O2 value is above 3%, then re-tune the burner all along its range of firing rates. Then continue to monitor the CO values to ensure long term safe operation of the burner at these more efficient
