Lennox gas furnaces, particularly the modern models, do not use traditional standing pilot lights. Instead, they employ more advanced and efficient ignition systems, such as intermittent pilot ignition and hot surface ignition.
What Ignition Systems Do Lennox Gas Furnaces Use?
1. Intermittent Pilot Ignition System
- This system uses an electronic spark to ignite the pilot light only when the furnace is called to heat.
- Once the pilot is lit, it proves the presence of the flame, and then the main burner ignites.
- This system is more efficient than a standing pilot because it only consumes gas when the furnace is operating.
2. Hot Surface Ignition System
- This is another common ignition system in modern Lennox gas furnaces.
- It uses an electrically heated element (similar to a light bulb filament) to ignite the gas.
- When the thermostat signals the furnace to start, electricity heats the igniter, which then ignites the gas.
- This system does not have a continuous pilot light and is more energy-efficient.
What are the Differences Between Electronic Ignition and Hot Surface Ignition?
Electronic Ignition
- This system typically uses a spark to ignite the pilot or main burner directly.
- It is often used in intermittent pilot systems where the spark ignites the pilot, which then proves the flame before the main burner lights.
- Example: In some Lennox models, the ignition control board generates a spark to light the pilot, which then proves the flame before the main gas valve opens.
Hot Surface Ignition
- This system uses an electrically heated element to ignite the gas.
- It is commonly used in modern furnaces because it is more efficient and reliable than traditional pilot lights.
- Example: The Lennox furnace with a hot surface igniter warms up for a specified period (e.g., 20 seconds) before the gas valve opens for a trial ignition. The igniter remains energized during the initial seconds of the trial ignition.
How Does a Lennox Gas Furnace with Hot Surface Ignition Operate?
- Startup Cycle:
- The thermostat signals the furnace to start.
- The igniter begins to heat up.
-
After a pre-purge period, the igniter warms up, and then the gas valve opens for a trial ignition.
-
Ignition Process:
- The heated element ignites the gas directly.
-
Once the main burner is lit, the system ensures the flame is present before continuing to operate.
-
Safety Features:
- Modern Lennox furnaces include various safety switches and sensors to ensure proper operation and prevent hazards such as gas leaks or explosions.
- These include combustion air pressure switches, rollout switches, and primary limit switches.
What are the Technical Specifications of a Lennox Gas Furnace with Hot Surface Ignition?
- Lennox Model ML193UH090XP36C-05:
- This model uses a hot surface ignition system with a 120V hot surface igniter.
- The startup cycle includes a 15-second pre-purge period, followed by a 20-second igniter warm-up phase, and then a 4-second trial for ignition.
