I have my oil burner serviced and cleaned every year. At the end of every cleaning, the tech gets an efficiency reading by sticking (what looks to me) like a meat thermometer, in the flue. He writes that number down on a card, hangs it on the wall, and says see you next year. I don’t want to know anything about the boiler. If I have a problem, I call and the guy is here within the hour. I was looking at the cards he leaves every year and I noticed that the rating seems to go down every year. I see a high of 89 several years ago, and my last one was 83. Some years it stays the same…never goes up.
Over the years, if I’m not mistaken, EVERY moving part of this system has been replaced with a new part…circulators, transformers, cad switch, ignition switch, motor (5 times) etc. (I am looking at receipts) So, it’s like ‘new’ all the time. What, exactly is causing the downward spiral in the efficiency rating?
Efficiency rating is determined by much more than using the “meat thermometer”. A similar device, he is indeed measuring stack temperature, e.g. the temperature of flue gases rising from the furnace or boiler. To determine true efficiency, he must also pull a smoke test through filter paper to gauge smoke density, and also measure the amount of CO[sub]2[/sub] in the flue gas. All three measurements are used to interpolate efficiency.
If the technician is using an electronic sensor, then it may need to be recalibrated. The older test sets, such as the one I own have a reagent fluid which has a finite life to determine the CO[sub]2[/sub] , and improper measurements can result from expired juice.
Among the parts listed, I don’t read about a new nozzle. They wear, effectively increasing the gallons per hour sprayed into the firebox, and should be replaced as part of an annual service plan.