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An Overview of Gas Furnace Ignition Systems

October 28, 2020

A strong argument can be made that the ignition system is
the most important component of any gas furnace. Even if every other part of
your furnace is working flawlessly, you won’t get any heat if it can’t burn
fuel in the first place.

Gas furnaces use a few different ignition systems today. If
you understand the differences between them, this will let you know what to
expect when your current furnace needs repairs — and it will help you make a
more informed decision when you choose a new furnace. Here is an overview of
gas furnace ignition systems.

Standing Pilot Light

The standing pilot light was the first ignition method used
in furnaces and other fuel-burning appliances. As the name suggests, a standing
pilot light remains lit 24/7 as long as the ignitor receives a steady supply of
gas. When the furnace starts up, valves open in the heat exchanger and gas
ignites as it comes in contact with the standing flame.

Standing pilot lights suffer from a few drawbacks, which
inspired the creation of new ignition systems to overcome them. For example, a
standing pilot can go out relatively easy, especially if a gap is present in
the furnace housing that allows circulating air to reach the inside of the
unit. Standing pilot lights are also not very energy-efficient, as the constant
use of gas to keep the pilot lit adds up over time.

If your furnace still has a standing pilot light, you may
want to consider a furnace upgrade in the near future. Standing pilot lights
are rare on furnaces manufactured in the last two decades, so if your system
still has one, it could be near the end of its effective life.

Intermittent Pilot Light

The most obvious way to improve the standing pilot light was
to find a way to use it only when needed so that you can conserve the fuel
previously used to keep it burning constantly. This is the principle behind an
electronic intermittent pilot light.

Intermittent pilot lights work by using sensors and a
thermocouple to monitor gas ignition and the condition of the pilot light. When
your thermostat signals for your furnace to turn on, an electrical spark is
created to light the pilot light. The sensor detects whether the gas ignited properly,
and if so, shuts the valve to extinguish the pilot light.

With an intermittent pilot light, you don’t have to manually
relight the pilot light to get warm air from your furnace again. However, the
drawback for intermittent pilot lights is that these electronic ignitors are
more complex and may be more expensive to service and repair. Since the pilot
light doesn’t stay lit, it can also be harder to pinpoint the ignitor as the
source of a problem with your furnace.

Hot Surface Ignition

The most recent advancement in gas furnace ignitors is
direct hot surface ignition. Rather than igniting the gas in your burner with a
flame, a conductive surface is heated to a temperature above the ignition point
of the gas; the conductive surface is usually a ceramic rod. Once the ignitor
sensor detects the burner flame is lit, the ignitor control board stops sending
current to the ignitor to allow it to cool.

Hot surface ignitors are thought to be safer than other
types of pilot lights since no open flame is present. The ceramic rod in a hot
surface ignitor glows red when your furnace starts up, so you can easily tell
if the ignitor is heating properly. Like intermittent pilot lights, hot surface
ignitors are complex devices that a technician must service.

The ignitor is an essential component of every gas furnace
that many homeowners don’t think about. Consider the ignitor type when you’re
in the market for a new furnace, and contact us at Comfort Solutionsfor
ignitor repair or any other HVAC service needs.