Heating fuel is any energy source burned or converted to warm buildings and heat water. The term most often refers to No. 2 heating oil, a petroleum-based liquid delivered by truck and stored in tanks at homes and businesses. But it also covers natural gas, propane, electricity, and wood, all of which serve the same purpose through different equipment. In the United States, heating oil is especially common in the Northeast, where millions of homes rely on it as their primary heat source.
How Heating Oil Differs From Other Fuels
No. 2 heating oil is a distillate fuel, meaning it’s refined from crude oil through a distillation process. It’s closely related to diesel fuel and shares a similar chemical makeup: hydrocarbons in the C11 to C20 range, with roughly 69 to 79 percent paraffins and 19 to 25 percent aromatic hydrocarbons. The practical difference between heating oil and diesel is mostly about how each is taxed and regulated, not what’s in the barrel.
Where heating oil really stands apart is in energy density. One gallon of heating oil contains about 138,500 BTUs (British Thermal Units), which is a measure of how much heat energy a fuel can produce. For comparison, one gallon of propane delivers roughly 91,452 BTUs, about 34 percent less. Natural gas is measured differently, at around 1,036 BTUs per cubic foot, or 100,000 BTUs per therm. That high energy density is one reason heating oil remains popular in cold climates: gallon for gallon, it produces more heat than most alternatives.
Common Types of Heating Fuel
- No. 2 heating oil: A liquid petroleum distillate stored in on-site tanks. Used in boilers and furnaces for space heating and in some water heaters.
- Natural gas: Delivered through underground pipelines. The most widely used heating fuel in the U.S. overall, though pipeline access varies by region.
- Propane: A compressed gas stored in tanks on your property. Common in rural areas without natural gas lines.
- Electricity: Powers heat pumps, baseboard heaters, and radiant systems. One kilowatt-hour equals 3,412 BTUs.
- Wood and pellets: A cord of wood contains roughly 20 million BTUs. Used in stoves and some boiler systems, particularly in rural homes.
Storage and Delivery
If your home uses heating oil, you’ll have a storage tank either in your basement, garage, or outside. The standard residential size is 275 gallons, available in vertical or horizontal layouts. Larger homes or those in especially cold regions sometimes use 330, 500, or even 1,000-gallon tanks. Most are made of steel or fiberglass.
Unlike natural gas, which flows continuously through a utility’s pipeline, heating oil requires scheduled deliveries from a fuel dealer. Many homeowners sign up for automatic delivery plans that estimate usage based on weather and past consumption, so the tank gets refilled before it runs low. Running a tank completely empty can pull sediment into your burner and cause system problems, so keeping it above a quarter full is a good habit.
How Long Heating Oil Lasts in Storage
Standard heating oil stays usable for about 18 to 24 months in a well-maintained tank. That means leftover fuel from one winter will typically carry over to the next season without any issues. Over time, though, the fuel can degrade. Water condensation inside the tank encourages bacterial growth, and those microorganisms break down the oil and produce sludge that clogs filters and nozzles. The condition of the tank itself matters too: rust and corrosion introduce contaminants. Some fuel dealers add stabilizing additives during delivery to extend the oil’s effective lifespan.
Environmental Standards and Sulfur Content
Heating oil has gotten significantly cleaner over the past decade. Historically, it could contain up to 2,000 parts per million of sulfur. Today, ultra-low sulfur heating oil (with less than 15 ppm) is the standard across much of the Northeast. New York led the shift in 2012, and states including Connecticut, Maine, Massachusetts, New Jersey, and Vermont followed with their own mandates. Lower sulfur content reduces particulate emissions and also helps heating equipment run more efficiently with less buildup inside the system.
Bioheat: The Renewable Blend
A growing share of heating oil now includes biodiesel, a renewable component made from sources like soybean oil or recycled cooking grease. These blends are marketed as Bioheat fuel. The naming convention is straightforward: B5 means 5 percent biodiesel and 95 percent heating oil, B20 means 20 percent biodiesel, and so on.
Under the ASTM 396 specification, every gallon of heating oil sold in the U.S. can contain up to 5 percent biodiesel without any equipment modifications. Blends at or below B5 are considered functionally equivalent to conventional heating oil, so your existing boiler or furnace handles them without adjustment. Higher blends (B20 and above) may require compatible seals and gaskets, though many modern systems already meet those requirements. Connecticut, for example, has required a minimum B5 blend since July 2022, with a mandate that the biofuel component achieve at least a 50 percent reduction in lifecycle greenhouse gas emissions compared to petroleum alone.
Cost Factors That Affect Your Bill
Heating fuel prices fluctuate based on crude oil markets, seasonal demand, and regional supply. Winter months bring the highest prices for heating oil and propane because demand spikes while supply chains face weather-related disruptions. Geography plays a role too: homes farther from refineries or distribution terminals typically pay more per gallon due to transportation costs.
Your actual heating costs depend on more than just fuel price. The efficiency of your furnace or boiler, the insulation in your home, thermostat settings, and local climate all factor in. A well-maintained, modern oil burner converts a higher percentage of each gallon’s 138,500 BTUs into usable heat, while an older system might waste 15 to 20 percent of that energy up the chimney. If your equipment is more than 15 to 20 years old, upgrading to a high-efficiency unit can meaningfully reduce how many gallons you burn each season.