Furnaces
How Do Oil Furnaces Work?
By Tom Moor•January 10, 2025When the cold weather sets in and temperatures drop, homeowners rely on a dependable heating system to keep their families warm, safe, and comfortable. While several types of heaters are available – including boilers, heat pumps, and gas furnaces – one option that doesn’t always get as much attention is the oil furnace. HVAC.com explains how oil furnaces work, outlines their pros and cons, and details the maintenance needed to keep them running safely and efficiently throughout the winter.
How Common Are Oil Furnaces?
Oil furnaces are less common than gas or electric heating systems but remain prevalent, particularly in the Northeast U.S. According to the U.S. Energy Information Administration (EIA), about 5 million homes nationwide rely on oil for heating, with 82% of them located in states like Maine, New Hampshire, and New York. This is largely due to the fact that many homes in the region were built before natural gas pipelines became widely available, making oil the go-to heating option.
How Does an Oil Furnace Work?
An oil furnace operates similarly to a gas furnace, but the key difference lies in the fuel and ignition process. Gas furnaces use natural gas or propane, which is ignited by a spark or flame, and are generally more efficient since natural gas burns cleaner.
Oil furnaces, meanwhile, use heating oil to heat homes. The oil is stored in a large tank, typically in the basement or garage, where it is pumped into the furnace and ignited in a combustion chamber. The resulting heat warms the air, which is then circulated throughout the home by ductwork or radiators.
Pros and Cons of Oil Furnaces
Pros:
- Independence from Gas Lines: Since homes with oil furnaces aren’t reliant on natural gas pipelines, they’re an ideal solution in rural or remote areas where gas service isn’t available, as well as in older homes.
- Longer lifespan: With proper maintenance and care, oil furnaces can last up to 25 years.
- High Heat Output: Oil furnaces tend to produce more heat per unit of fuel than gas furnaces, making them ideal for homes in colder climates.
- Safety: Oil furnaces are considered safer than natural gas furnaces because heating oil is non-combustible and doesn’t produce carbon monoxide or other poisonous gasses.
- Less Expensive Upfront. Oil furnaces are typically less expensive to buy and install than gas units.
Cons:
- Higher Operating Costs: Oil tends to be more expensive than natural gas, so oil furnaces can result in higher heating costs over time.
- Less Efficient: Oil furnaces are considered less efficient than their gas counterparts. Oil furnaces offer Annual Fuel Utilization Efficiency (AFUE) ratings between 80% and 90% while gas furnaces offer ratings between 89% and 98%.
- Maintenance Needs: Oil furnaces generally require more regular maintenance than gas furnaces, including cleaning the burners and checking the oil tank.
- Storage Space: A large oil tank is needed, which may take up considerable space in a basement, garage, or utility room.
- Delivery Required: Oil must be delivered to the home by a truck, making it less convenient compared to the automatic delivery of natural gas.
Oil Pricing and Availability
Typically, oil is more expensive than natural gas, and because it must be delivered to the home, there are additional delivery charges to consider. The cost of heating oil can fluctuate due to factors including global oil prices, weather conditions, and regional supply and demand.
According to the EIA, homes that use natural gas for heating will likely see a 1% increase in fuel bills compared to last winter, while homes heated by heating oil may see a 5% decrease.
Maintenance Requirements for Oil Furnaces
Like any heating system, oil furnaces require regular maintenance to ensure efficient and safe operation. One of the most important tasks is cleaning the burners, heat exchanger, and flue, as dirt, soot, and debris can accumulate, reducing efficiency and potentially causing malfunctions.
The oil filter should be replaced annually, usually during a fall tune-up, to prevent clogs. Additionally, the oil tank should be inspected for leaks, and the fuel supply monitored to avoid running out during the coldest months.
Other essential maintenance tasks include checking the flue pipe for holes, cracks, or leaks, inspecting moving parts for wear or damage, and examining electrical connections for safety.