How Does an Oil Burning Furnace Work?

The Basics of Oil Heating

Oil-burning furnaces use heating oil—a refined petroleum product—as fuel to produce heat. These systems are popular in areas without natural gas infrastructure, offering an effective and dependable heating solution.

The oil is stored in a tank and transported to the furnace as needed, ensuring you have a steady supply of heat.

Key Components of an Oil Furnace

Oil Tank

The oil tank stores the fuel, which is typically delivered by a supplier. Tanks can be located above ground, underground, or inside your home, depending on your setup.

A fuel pump transfers oil from the tank to the furnace burner to heat your home.

Burner

The burner is the heart of the furnace. It mixes oil with air and ignites the mixture to create a flame. The burner ensures the oil burns efficiently, providing consistent heat.

Combustion Chamber

The combustion chamber is where burner ignition happens. This insulated area contains the burning oil flames. The combustion chamber transfers heat to the heat exchanger.

Heat Exchanger

The heat exchanger absorbs heat from the oil flames in the combustion chamber and transfers it to the air that circulates through your home.

Blower Fan

The blower fan moves heated air through your home’s ductwork to distribute warmth throughout your house.

Flue or Chimney

The flue directs combustion byproducts, such as carbon dioxide and water vapor, safely out of your home.

How It Works: Step-by-Step

1. Fuel Delivery

When your thermostat signals a need for heat, the furnace activates. The fuel pump draws oil from the storage tank and delivers it to the burner.

2. Fuel Atomization

The burner sprays the oil in a fine mist, mixing it with air. This atomization allows the oil to burn more efficiently.

3. Ignition

An electric igniter or pilot light ignites the oil-air mixture, creating a controlled flame in the combustion chamber.

4. Heat Transfer

The heat from the flame warms the heat exchanger. Depending on your system, air or water absorbs this heat and carries it through your home.

5. Exhaust Removal

Combustion gases are vented through the flue, ensuring your indoor air remains safe and clean.

6. Heat Distribution

Heated air is blown through ductwork, maintaining a cozy indoor temperature.

Advantages of Oil-Burning Furnaces

Oil-burning furnaces offer these advantages over other types of furnaces:

• Reliability: Oil furnaces provide consistent heat even in extreme cold.
• High BTU Output: Oil produces more heat per gallon than natural gas or electricity.
• Energy Independence: With an oil tank, you control your fuel supply and aren’t dependent on utility grids.

Oil-Burning Furnace Maintenance

Follow this checklist to keep your furnace running smoothly throughout the heating season.

Refer to the owner’s manual for your furnace to find additional maintenance tasks needed for your unit and details on completing the maintenance steps described below.

1. Schedule Annual Professional Inspection and Maintenance

Scheduling professional furnace maintenance by a qualified HVAC technician yearly tune-up is essential to keep your heating system running smoothly and efficiently.

They’ll inspect, clean, and test critical components, ensuring everything works as it should. A professional inspection typically includes:

• Cleaning the combustion chamber.
• Checking the burner nozzle for wear or clogging.
• Testing the efficiency of the heat exchanger.
• Calibrating the thermostat for accuracy.

2. Replace or Clean the Oil Filter

The oil filter prevents dirt, debris, and sludge from reaching the burner. Over time, the filter can clog, reducing fuel flow and causing the furnace to work harder. Replace or clean the filter at least once a year or as recommended by the manufacturer. This is especially important if your fuel tank is older, as sediment tends to accumulate.

3. Inspect the Oil Tank

Examine the oil tank for signs of rust, corrosion, or leaks. Ensure the tank’s vent and fill pipes are clear of obstructions. If you notice unusual smells, oil puddles, or rapid fuel loss, contact a furnace repair professional immediately to address potential issues.

4. Clean or Replace the Air Filter

Check the air filter monthly during the heating season. A clogged air filter restricts airflow, reducing efficiency and straining the blower. Replace or clean the filter every 1–3 months, depending on usage and the type of filter.

5. Check the Burner and Nozzle

The burner assembly is critical for proper combustion. Inspect the burner for soot, dirt, or oil residue, which can indicate incomplete combustion or clogged nozzles. Cleaning or replacing the nozzle ensures the oil is atomized efficiently, optimizing performance.

6. Monitor the Flue and Chimney

Inspect the flue pipe and chimney for blockages, cracks, or excessive soot buildup. These components carry exhaust gases out of your home, so keeping them clear and secure is essential for safety. If you notice damage or obstructions, call a furnace repair professional for repairs.

7. Test the Thermostat

The thermostat controls your furnace's operation, so it’s important to ensure it’s functioning properly.

Test the thermostat’s accuracy by comparing the displayed temperature with a separate thermometer.

Replace an old or faulty thermostat with a programmable or smart model to improve energy efficiency.

8. Bleed the Fuel Line (if necessary)

If your furnace has been off for a while or you’ve recently run out of oil, air may enter the fuel line, causing the burner to sputter or fail to ignite. Bleeding the fuel line removes trapped air, but this task should only be performed by someone familiar with the process, as it involves handling flammable materials.

9. Lubricate Moving Parts

Some furnaces have motorized components that require periodic lubrication to reduce friction and wear. Check your owner’s manual for guidance on which parts to lubricate and the type of oil to use.

Proper maintenance of your oil-burning furnace is the key to reliable, efficient, and safe operation. By following the tips in this guide and scheduling annual professional inspections, you can ensure your furnace stays in great shape for years to come. Not only will this save you money, but it will also provide the peace of mind that your home will stay warm and cozy all winter long.