What is a hot surface igniter?

In 1993, the furnace industry moved away from the standing pilot light ignition system in all furnaces. One of the most popular styles of ignition used today is a Hot Surface Igniter (HSI). The first HSI’s looked like a “fork” and were a silicon carbide material. While this type of igniter is very dependable, they are fragile. The newer style HSI is made out of Silicon Nitride, which is a more durable material. This is the type of igniter that our technicians stock on their trucks. While they are more expensive to purchase up front, you can expect a longer life out of them.

Both types are designed for 100,000 cycles, but most never last that long. HSI’s heat up to surface temperatures of 1800 degrees up to 3100 degrees Fahrenheit. Any contaminants that find their way to the surface of the igniter will get burned on to the surface and create hot spots. Contaminants could include sealants, fiberglass insulation and dust. Condensation dripping onto the igniter from a clogged drain line or rusted coil will also shorten its life.

We find the HSI’s on 90% plus efficient furnaces have a lower fail rate than an 80% furnace. This is due to the combustion air being brought in from the outside on the 90% furnace rather than drawing it from the house. This is especially true if your furnace is located near your clothes drier.