How Does a Furnace Work?

The Heating Cycle

Understanding the heating cycle of a furnace is essential for homeowners who want to ensure their heating system is working efficiently. Let's take a closer look at how a furnace works, step by step.

1. Thermostat Activation

The heating process begins with the thermostat, which acts as the control center for your furnace. When the temperature in your home drops below the thermostat setting, the thermostat sends a signal to the furnace to start the heating cycle.

2. The Draft Inducer Fan Starts

The draft inducer fan pulls air into the combustion chamber for ignition. Without an adequate air supply, the furnace burners won’t light.

3. Burner Ignition

If all safety interlock switches and controls indicate that the furnace is ready for safe ignition, the burner valve opens to supply gas to the burner tubes. For models with a pilot light, a small flame constantly burns and ignites the gas flowing through burners. Most current-day models use an electronic igniter to light the burner.

4. Heat Transfer

Once the burner ignites, it creates heat by burning the gas. The heat exchanger captures the heat produced by the burning gas and transfers it to the air that gets blown over the heat exchanger tubes by the indoor circulation fan. The warm air goes up and out of the heat exchanger and into the rooms of the house through air ducts.

5. Combustion Ventilation

Combustion also produces byproducts like carbon dioxide and water vapor. A flue or vent expels combustion byproducts safely outside, ensuring the air inside remains clean. The draft inducer fan helps blow combustion gasses up through the flue.

6. Cycling to Maintain Set Temperature

Once the thermostat reaches the desired temperature, the control shuts the gas supply off, stopping the heating process. The ignition and heating cycle repeats as the thermostat detects decreases in room temperature.

Understanding the heating cycle of a furnace helps you identify potential issues and ensure their system is running smoothly.

Regular furnace maintenance and inspections by professionals can also help extend the lifespan of your furnace and improve its efficiency.

Parts of a Furnace

Knowing about the different parts of a furnace can help you maintain it properly and troubleshoot any issues that may arise.

• Burner: The metal assembly where gas is ignited to produce flames.
• Draft Inducer: The draft inducer is a fan that draws ambient air into the gas burner combustion chamber and carries combustion exhaust air out through the exhaust flue to the outside of your home.
• Heat Exchanger: Transfers heat from the gas burner flame to the air.
• Pilot Light or Igniter: Used to ignite the gas at the burner.
• Thermostat: Senses temperature inside your home and cycles the burner on and off to regulate indoor temperature.
• Blower Fan: Blows air through the heat exchanger and then distributes the warmed air throughout the home.
• Vent or Flue: Safely directs combustion byproducts, such as carbon dioxide and carbon monoxide, to the outside of your home.

Furnace Maintenance and Safety

Follow these expert tips to maintain your furnace and operate it safely.

Furnace Maintenance

Regular furnace maintenance is crucial for smooth performance and to ensure the safety of your home. By following a few essential tasks, you can keep your furnace running smoothly and efficiently.

Firstly, it is important to regularly replace the furnace filter. A clogged or dirty filter can restrict airflow and strain the system, leading to reduced efficiency and potential breakdowns. Check the filter monthly and replace it every three months or as recommended by the manufacturer.

Another vital maintenance task is to clean the furnace's blower assembly. Over time, dust and debris can accumulate on the blower wheel and motor, affecting airflow and causing excessive noise. Carefully remove the blower assembly cover and use a soft brush or vacuum cleaner to remove any buildup.

Inspecting and cleaning the furnace's ductwork is also essential. Dust, pet dander, and other particles can accumulate in the ducts, reducing airflow and indoor air quality. Consider scheduling professional duct cleaning every few years to maintain a clean and efficient system.

While performing maintenance tasks, it is essential to be aware of signs that indicate a malfunctioning furnace. These signs may include strange noises, uneven heating, frequent cycling, or an increase in energy bills. If you notice any of these issues, schedule furnace repair service to have a Sears Home Services professional HVAC technician diagnose and repair the problem.

For safety, schedule professional furnace maintenance every fall to prepare the unit for winter. A fall furnace tune-up by a certified technician will help prevent malfunctions and unexpected breakdowns. It will also improve efficiency and help your furnace last longer.

Here’s a helpful video that shows how a Sears Home Services technician tunes up and maintains a furnace for winter:

Safety Tips for Using a Furnace

Always prioritize safety when operating a furnace. Follow these tips to safely operate your furnace.

• Ensure that the area around the furnace is clear of flammable materials and avoid storing items in close proximity.
• Install carbon monoxide detectors near the furnace and throughout your home to alert you of any leaks.
• If your heater has a pilot light, regularly check it to make sure it’s blue. A yellow or orange flame may indicate a ventilation problem.
• Replace the air filter regularly as recommended in the owner’s manual.
• Regularly check that furnace vents are clear and unblocked.

Whenever you notice problems with your furnace, immediately schedule repair service. We’re standing by with experienced Sears Home Services HVAC technicians to fix any type of furnace failure that comes your way.

Trust Sears Home Services to help you keep your home warm and safe all winter long.