Once upon a time, when people discussed gas furnaces, they often talked about the pilot light. This flame burned through the winter in the furnace, ready to ignite the burners as soon as gas started to flow to them. Sometimes the pilot light would go out and need relighting—and this was often Troubleshooting Step #1 on lists of what to do if a gas furnace stopped working.
But now the question people are asking isn’t “how to light a gas furnace in Fresno, CA” so much as wondering what happened to the pilot light. Some models may still use them, but not many. The pilot light has gone out of fashion, and for some good reasons.
Energy Efficiency
The main reason for the vanishing of the pilot light is the increasing concern about energy efficiency. Furnaces have made significant advances in how much energy they use: where it was once normal to see furnaces with ratings of 70% AFUE (meaning the furnace turns 70% of its fuel source into heat and loses the rest to exhaust), today’s furnaces often have AFUE in the 90s. Part of this comes from eliminating the pilot light.
A pilot light has to remain lit during the winter to do its job. Anybody who’s had to re-light a failed pilot light can tell you it’s an annoyance. The pilot light is a continual use of natural gas, which lowers the efficiency of the unit as it burns gas whether the furnace is running or not. A standing pilot light can drain an extra $10 a month. Getting rid of the need for pilot lights takes away this unnecessary drain.
Reliability
Pilot lights used to go out all the time, and getting them relit was a chore—and it wouldn’t work all the time either. The new ignition systems are much more dependable so people can trust their furnace will actually turn on when they need it.
Safety
Using a pilot light in a furnace has several potential dangers. If a pilot light goes out and the gas valve for the furnace remains open, gas can slowly accumulate within the combustion chamber. This poses a significant safety hazard, as any spark or ignition source in the area could lead to an explosion. Pilot lights don’t have advanced sensors or controls to manage situations like this.
Electronic Ignition
What replaced the standing pilot light? What’s the new “fashion”? It’s electronic ignition systems. The most common type is called a hot surface igniter. With these igniters, an electrically heated element (similar to the filament in a lightbulb) ignites the gas burner when the thermostat requests heat. These systems are common in high-efficiency furnaces because of their quick response time and efficient energy use.
The other type of electronic ignition system is the intermittent pilot light, which are found in mid-efficiency furnaces. This type of ignition system uses an electronic control module to ignite a pilot light only when the furnace is about to start heating. The pilot light goes out after the burners are lit.
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