During the past several years, new-style silicon nitride igniters for furnaces and boilers have taken over the industry. Virtually all new residential gas furnaces now feature the new technology.
In the replacement parts market, there are a plethora of silicon nitride igniters available to take the place of the old-style silicon carbide igniters. This represents both new opportunities as well as new challenges.
I personally know several technicians who only carry these universal silicon nitride igniters on their vans. If they have not yet had problems as a result, I think they soon will. What follows is a treatise on why technicians may want to think twice before blindly installing a universal SiNi replacement igniter on every service call.
A hot surface igniter is electrically similar to an incandescent light bulb filament — only much heavier and larger. When there is a demand for heat, the igniter is energized with 120 volts and it glows red-hot. The gas is released, and the hot surface of the igniter lights the gas.
The hot surface igniter started being used in place of spark ignition in residential gas-fired furnaces as early as the early 1990s. Advantages of hot surface igniters over spark ignition were: The elimination of the pilot burner and associated parts. Quieter operation. Spark generators can mess with radio or TV reception, and also mess with arc flash circuit interrupters (which have now become code in many areas). Plus, the surface area of the igniter is much larger than a tiny spark. This leads to more reliable ignition and a safer system.
‘Gray and sparkly’
Hot surface igniters were originally all made of a substance called silicon carbide, which is a gray and sparkly material. The same material is also used to make artificial whetstones for sharpening knives. The mounting base was made of nonconductive ceramic. One of the disadvantages of this material was that it is very brittle and requires delicate handling. If you drop one, you will only do it once because it will shatter like glass.
Silicon carbide igniters have a limited life span, and, as they age, they tend to crack and break. This tends to be a very common cause of no heat calls and many technicians are used to looking at the igniter for a crack on every call.
While the silicon carbide igniter was engineered to last the full life of a furnace, due to typical issues that lead to short cycling, typical igniter life is in the eight- to 12-year range.
In the late 1990s and early 2000s, some manufacturers started using silicon nitride igniter technology, with Lennox and Trane being early adopters.
One of the advantages of the new material was that the igniters were tough and had an extremely long lifespan. Over time, more and more manufacturers began switching to the SiNi technology and touting the long lifespan of their igniters. These SiNi igniters could not be used in retrofits.
Right around 2012, a major player in the industry introduced the first universal SiNi igniter designed to replace the old silicon carbide igniters in existing installations. The marketing touted long life and universal applications, which seemed like a great advantage. Now there are at least four competing versions of universal SiNi replacement igniters available.
I’m not going to tell anyone to never use one, but I do want to discuss the disadvantages and suggest that they are definitely not a one-fits-all replacement option.
Please note that at the time of this writing, all universal SiNi replacement igniters are only meant to replace the old-style silicon carbide igniters. They cannot be used to replace original equipment manufacturer silicon nitride igniters on newer furnaces.
The problem comes from igniter positioning. When the furnace was originally designed, the engineers made some pretty important decisions about where to put that silicon carbide igniter in relationship to the end of the burner. This positioning is critical to the successful and immediate ignition of the fuel/air mixture.
The new universal igniters have a much smaller surface area, and, by default, the overall position overall position of the igniter changes. In this respect, the engineers are totally left out of the process and the decision rests solely on the technician. This new position may not be ideal, and misfires and delayed ignition may result.
HVAC construction technicians run into problems when they approach the installation of the new SiNi igniter the same way they approached the old silicon carbide style—which is to put it in, turn it on and leave. With the new igniter being smaller and in a slightly different position, just because it lit once doesn’t mean it will continue to do so on time, every time. You need to be much more careful and ideally cycle the furnace between 30 to 50 times without a single hiccup or ignition failure to have some sense of surety that the system will continue to be safe and reliable after your tail lights fade from view.
I have been on several late night calls within weeks of a universal igniter installation where the customer complained their furnace was making banging or popping sounds. That was the sound of delayed ignition causing a buildup of fuel and air to explode as it lit seconds later than it should have.
I recommend you use an OEM-style silicon carbide Igniter installed in exactly the same way as the old one every time you can. You can sleep easy knowing you have not created any hidden delayed ignition issues that can surface later.
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