Combustion Theory and Optimization

How many heating contractors or technicians understand combustion? Not many. Now hold your fire, we're not saying they don't know their stuff; we're suggesting there is a lack of awareness in regard to the theory of combustion. Because we're well versed with oil and gas combustion, we believe we have some say on this subject. It's also a well known fact that an average oil technician knows a bit more than the average gas technician. Ironically, at this time, gas combustion tests are not required in the state of Massachusetts.

Most every person in the world of heating relies quite heavily on the old "net flue temperature and Co2" method of determining the combustion efficiency. Every oil burner technician out there at one point in time held a slide chart in his hand for the first time that enabled him to determine this. But, this is not Mother Nature. This slide chart was made by man. There is a succinct problem with this well-accepted practice: the lower the flue temp equates to a higher efficiency. Doesn't this defy physics? It does! Think about it: a heating appliance's role in life is to transfer heating energy into a heating medium (water or air). If the flue gas temperature is close to or even below the discharge temperature of the boiler or furnace, how on earth can heat be transferred? Well, it is, but the wrong way!

Here is how you know if your heating guy or gal knows their stuff: if they check the operation of your furnace, boiler, or water heater with digital combustion analyzer, you're in luck; they might know what they're doing! Unfortunately, this subject is simply not grasped by perhaps 95% of technicians. So enough with the small talk you say? Here's a trick question. What's more efficient: a 92% AFUE gas furnace with a o2 reading of 10.2% or an 85% AFUE oil fired boiler with an o2 ready of 5%? Oh, both appliances are the same BTU input. If you guessed oil, you're correct. How did you come to this?

Also, how do you know if the chimney is venting, or if there is enough combustion air? There's theory, like what the code book and installation manual says. And then there are real life conditions. Without good combustion training and good tools, there are a lot of unknowns. Some of these unknowns may impact your fuel bill. Some may be a little more serious.