Figure 3
burner. Keep in mind that all fuelburners are 100 % efficient. They burn 100 % of the fuel that comes out of that oil nozzle or gas spud and burn nothing when shutoff. What we want to know is how well the burner is converting the fuel to useful heat and Btus and how much help the heat exchanger is adding to the process.
A leak in the heat exchanger is a bad thing when we are working on a furnace and due to smells, fumes and soot we smoke-bomb them like crazy and go nuts to try to find the cause, but have you ever smoke-bombed a boiler? How about a water heater? Why not? If you have an air leak you have a draft leak and regardless of the heat exchanger it just isn’ t a good thing.
Many years ago, I was taught how to do this test and when we went nuts over efficiency in the 1970s it kind of got lost in the shuffle. That’ s too bad, because many of us remember it, but only use it when all else fails. In my opinion it should be done with every new unit and at every routine service. Do you know what test I’ m talking about? It’ s called the over-fire CO2 or“ True CO2” test and yes those of you with your electronic analyzers can do it too!
Although we’ re going to measure CO2 or O2 we are really measuring draft and so let’ s get on with it.
After setting up your burner for optimum performance, not efficiency, take one final reading of fluegas O2 or CO2 over-the-fire. I don’ t recommend inserting the curly end of a Fyrite sampling tube into the chamber and if you do that to an electronic unit you could damage the thermocouple on the end of the probe. In all cases use a short piece of hose that will connect to your sampling device and a piece of ¼” stainless or hard steel tubing. After obtaining the sample compare it to the breeching CO2 or O2 and there should be a small difference in the readings. The greater the difference, the bigger the air leak, Figure 3, and the more efficiency you’ re losing. Don’ t be afraid to check new units as I’ ve already said, equipment is assembled by people and we all can have a bad day.
The last thing to do is talk about the vent whether it’ s a chimney, powerventer, stub-vent or through the wall termination hood of a direct vent system you have to get that draft back outside, remember? With a chimney everyone seems to think it’ s a piece-of-cake, oh really? Well, chimneys are not what they used to be. Why? Because air flow( draft) has actually changed due to building and equipment technologies.
In my books we have a chart, Figure 4, that shows just how much draft can be produced at various temperature differences and has changed due to stack and chimney temperatures over the years.
Figure 5
But to give you the skinny on it, it basically shows that when you cut your draft temperature in half you cut your ability to make thermal draft in half and chimneys rely on thermal draft to work more than anything else.
When oilburners and heat exchangers produced 700 ° F at the breeching of the appliance life was good and-. 02” w. c. over-the-fire,-04” w. c. in the breeching even in the summer and it was a done deal! But, if you cut that temperature to 350 ° F, Figure 5, then the-. 02 becomes-. 01 and the-. 04 becomes-. 02 and you have a draft problem. By the way in Figure 4 the“ Old” burner” ran at about 1400 ° F in coal conversion equipment, the“ New” burner ran at 700 ° F and the“ Modern” is today’ s equipment at 350 ° F. This chart has been in use since 1907. Think about that! Most of this material comes from our Firedragon Academy textbook‘ Advanced Residential Oilburners’. See ya. l FON
George Lanthier is the owner of Firedragon Academy, a 35-year-old Massachusetts Certified School teaching both gas and oil and other heating subjects. Firedragon Academy has its training facility in Webster, Massachusetts. Firedragon is also a publishing firm publishing George’ s over 60 books and manuals on HVAC subjects. He is a CETP, ESCO, NATE, NORA, PMAA and PMEF Proctor and has been a Massachusetts Certified Instructor since 1975. His website can be found at www. FiredragonEnt. com
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