How Does a Furnace Work?

Keeping your home warm and comfortable is a top priority every winter. Your furnace is a key player in achieving this goal. Understanding how a furnace works helps you appreciate the comfort it provides and makes it easier to identify potential issues that may require professional furnace repair or replacement.

What is a Furnace?

A furnace is a heating unit that forms one part of your home’s heating, ventilation, and air conditioning system. Its primary function is to heat and distribute air throughout your home via ductwork. Furnaces can be powered in various ways, with the most common fuel sources being natural gas, electricity, and oil. Maryland households most often have gas furnaces, so that’s what we’ll focus on here.

You may have one of three primary types of gas furnaces in your home:

• Non-condensing furnaces are the traditional type with an annual fuel utilization efficiency (AFUE) rating of around 80 percent. This means they convert about 80 percent of the fuel they consume into usable heat for your home, while the remaining 20 percent is lost in the exhaust.
• Condensing furnaces are more efficient, with an AFUE rating of 90 to 98 percent. They achieve this higher efficiency by using a second heat exchanger to extract heat from the exhaust gases before venting them to the exterior.
• Modulating gas furnaces offer the highest efficiency and comfort level by continuously adjusting the fuel amount and blower speed. This results in more consistent indoor temperatures and quieter operation.

Key Furnace Components and the Heating Cycle

To understand how a furnace works, you must know its main components and their respective roles in the heating cycle.

• The thermostat is your HVAC system’s command center, signaling the furnace to power on when the temperature in your home drops below the desired setting.
• The control board manages the furnace functions, ensuring they work in harmony to heat your home safely and effectively.
• The igniter found in modern furnaces replaces the old pilot light. When the thermostat signals the need for heat, the igniter sparks to ignite the burner.
• The burner is where natural gas is ignited to produce heat. The burner is connected to the gas supply line and is controlled by the furnace’s electronic control system.
• The gas valve is a safety feature that controls the natural gas flowing into the burner. It only opens when the control board signals that all other components are functioning correctly. If no flame is detected, it signals the control board to shut down the gas supply.
• The flame sensor is a safety device that monitors the burner to confirm that it has ignited and is burning properly.
• The heat exchanger is a metal component that absorbs heat from the burning gas in the burner and warms the air blown across it. Condensing furnaces have two heat exchangers for maximum heat absorption.
• The blower pushes air across the heat exchanger. Once warmed, the blower propels the air into the ductwork, distributing it throughout the house.
• Plenums are boxes that serve as a hub for the ductwork. The supply plenum directs heated air into the ductwork, and the return plenum brings cool air back to the furnace for reheating.
• The air filter removes particles from the air before it’s heated and circulated back into your home. This protects the furnace’s internal components from dust and debris and helps improve indoor air quality.
• The flue or vent pipe safely vents combustion gases to the exterior.

Furnace Safety Tips

While furnaces have numerous safety features, homeowners should also play their part in maintaining a safe and efficient heating system. Here are some safety tips to remember:

• Schedule regular maintenance checks with an HVAC professional to keep your furnace working properly and safely.
• Keep the area around the furnace clear to reduce the risk of fires.
• Install carbon monoxide detectors to notify you of any CO gas leaks that could harm your family and signal a problem with your furnace.
• Check your air filter monthly and replace it as needed to maintain optimal airflow and indoor air quality.
• Regularly check your flue pipe for obstructions that may cause dangerous backdrafting.
• Don’t ignore strange noises or smells. These could be signs of potential issues, so have a professional inspect your furnace as soon as possible.

Furnace Services in Pasadena, MD

Universal Air Conditioning and Heating is a reliable HVAC professional dedicated to your comfort and safety. We have over 35 years of experience installing, repairing, replacing, and maintaining furnaces and other HVAC systems, so you can trust us to deliver prompt, professional service. If you’re in Pasadena, MD, or the surrounding area, please contact us at 410-544-7334 to arrange the heating and cooling services you need.