What Is Heating Oil? And How It Differs From Diesel
Heating oil is No. 2 fuel oil, made for burners. Diesel is its engine-grade twin. Same part of the barrel, same red dye when untaxed, different specs and rules.
Heating oil is No. 2 fuel oil: a middle distillate made to ASTM D396 for furnaces and boilers. No. 2 diesel comes from the same cut but is made to ASTM D975 for engines, with a cetane minimum. Both are dyed red when sold tax-free. Most Northeast states require 15 ppm sulfur heating oil; several also require Bioheat blends.
General information on fuels, not tax or legal advice. Dye, tax and fuel rules vary by state and change; check with your state agency or a tax professional.
What is heating oil?
Heating oil is a distillate fuel oil burned to make heat. EPA's fuel rules define it as a fuel "used, intended for use, or made available for use in furnaces, boilers, or similar applications," and add that kerosene and jet fuel are not heating oil. In the trade, "heating oil" almost always means No. 2 fuel oil. EIA describes it as a distillate for atomizing burners in home heating and medium-sized commercial and industrial burners.
The grades come from ASTM D396, the fuel oil standard:
| D396 grade | What it is | Where it's burned |
|---|---|---|
| No. 1 (S15, S500, S5000) | Light distillate, close to kerosene. Pour point 0°F max. | Vaporizing burners, and tanks where the oil has to stay fluid in the cold |
| No. 2 (S15, S500, S5000) | The standard heating oil. Pour point 20°F max. | Home furnaces and boilers, small and medium commercial burners |
| B6–B20 (S15, S500, S5000) | Heating oil blended with 6–20% biodiesel. Added to D396 by an ASTM vote in December 2014. | The same burners as No. 1 and No. 2 |
| No. 4, No. 5, No. 6 | Heavier residual-type oils | Larger commercial and industrial boilers. Several cities and states have phased these down. |
The S number is the sulfur limit in ppm: S15 is 15 ppm, S500 is 500 ppm, S5000 is 5,000 ppm. Pour points from the D396 table as adopted in Maryland's fuel rules (COMAR 03.03.05.04).
Who uses it? EIA counts about 4.79 million U.S. households heating with oil in the winter of 2023–2024, about 82% of them in the Northeast. Commercial buildings burn it too, for space and water heating and in combined heat and power plants. Buildings with oil heat can also have diesel generators, which is where the two fuels get confused.
Head to headHeating oil vs diesel: the specs side by side
EIA classifies distillate fuel oil as one petroleum fraction, "including diesel fuels and fuel oils." Refiners make No. 2 diesel and No. 2 heating oil from the same cut of the barrel, and one futures contract (NYMEX NY Harbor ULSD) is the benchmark for both (see the diesel price report). The specs are where they differ:
| Property | No. 2 heating oil | No. 2 diesel (incl. off-road) |
|---|---|---|
| Standard | ASTM D396, for burners | ASTM D975, for compression-ignition engines |
| Cetane | No minimum | 40 minimum (federal ULSD rule: cetane index 40 or no more than 35% aromatics) |
| Flash point | 100°F (38°C) minimum | 125°F (52°C) minimum |
| Viscosity at 40°C | 1.9–3.4 cSt | 1.9–4.1 cSt |
| Sulfur | Set by the state. 15 ppm in NY, NJ, MD and New England; D396 still has 500 and 5,000 ppm grades | 15 ppm nationwide for on-road and nonroad diesel (EPA) |
| Biodiesel | Required in NY, NYC, CT and RI heating oil (Bioheat) | Set by fuel specs and the engine maker, not by heating oil laws |
| Energy | 138,500 Btu/gal (EIA) | 137,381 Btu/gal (EIA) |
| Weight | About 7.0–7.1 lb/gal | About 7.1 lb/gal |
| Color | Red when sold untaxed; can be undyed if taxed | Off-road: red. On-road: undyed |
Flash point, viscosity and cetane from the D396 and D975 tables as adopted in COMAR 03.03.05.02 and .04; ULSD standard from 40 CFR 1090.305. Btu figures from EIA, which updates them each year. Weights from our diesel weight guide. Grade 1 vs 2 is covered in diesel #1 vs #2.
What the differences mean in practice: cetane measures how readily fuel ignites under compression. A burner lights its fuel with a spark and doesn't care about cetane, so D396 doesn't set one. An engine does. Diesel's higher flash point makes it a bit less volatile, and D975 allows diesel to be thicker than D396 heating oil. For cold weather the numbers that matter are the same for both: No. 2 heating oil can have a pour point as high as 20°F, and No. 2 diesel typically clouds at 6–14°F. Both need protection in outdoor tanks (see what temp does diesel gel?).
The merged questionHeating oil vs off-road diesel
This is the pair people mix up most, because they look identical. Off-road diesel is ordinary ultra-low sulfur No. 2 diesel with red dye added. EPA has held diesel for nonroad engines to 15 ppm sulfur since 2010, and fuel for locomotives and marine engines since 2012. Heating oil is No. 2 fuel oil made to D396, and its sulfur limit depends on the state.
Where they match
- Same dye. Federal tax law treats No. 1 and No. 2 fuel oil as diesel fuel (only No. 5 and No. 6 are excluded), so both need the IRS red dye, Solvent Red 164, to leave the terminal untaxed.
- Same tax status. Neither one pays the 24.4¢ federal highway tax when used for a nontaxable purpose. Heating is a nontaxable use.
- Same base. Both are No. 2 distillates with nearly the same energy and weight.
Where they don't
- Spec. Off-road diesel meets D975 and the federal 15 ppm diesel standard. Heating oil meets D396.
- Cetane. Off-road diesel is certified for engines. Heating oil isn't.
- Sulfur outside the Northeast. Off-road diesel is 15 ppm everywhere. Heating oil can be higher where no state rule applies.
- Biodiesel. Heating oil laws in NY, CT and RI require a Bioheat blend. They don't apply to fuel for engines.
Older articles, including an earlier version of this page, said off-road diesel carries more sulfur than heating oil. That stopped being true in 2010. Today off-road diesel is held to 15 ppm everywhere, while heating oil is held to 15 ppm only where a state requires it.
Can you swap them?
| Situation | Verdict | Why |
|---|---|---|
| Off-road diesel in an oil burner or boiler | Usually OK | EPA lets a batch certified as ULSD also be designated heating oil "if it is also suitable for such use." Heating isn't a taxable use, so dyed fuel is fine there. Check the burner maker's fuel spec, because D975 allows diesel up to 4.1 cSt and D396 tops out at 3.4. In Bioheat states, fuel sold as heating oil must carry the required blend. |
| Heating oil in a diesel generator | No | Since October 1, 2010, stationary diesel engines covered by EPA's engine standards (40 CFR 60 subpart IIII, under 30 liters per cylinder) must burn nonroad diesel: 15 ppm sulfur and cetane index 40 or no more than 35% aromatics. Heating oil isn't certified to that. After Hurricane Sandy, New Jersey let critical facilities use home heating oil in emergency generators from October 30 to November 13, 2012, by enforcement discretion. It warned that higher-sulfur heating oil may damage model year 2012 and later engines of 175–700 hp. |
| Heating oil in construction or farm equipment | No | Nonroad engines are built for 15 ppm diesel that meets D975, and heating oil isn't certified as either. Higher-sulfur heating oil may damage parts of newer engines (NJDEP, 2012). Check the engine maker's fuel spec. |
| Either one in a highway vehicle | No | Both are dyed, untaxed fuels. Highway use is a taxable use. See off-road diesel compliance and dyed vs clear diesel. |
Ultra-low sulfur heating oil (ULSHO)
Ultra-low sulfur heating oil is heating oil with no more than 15 ppm sulfur, the same limit as on-road and nonroad diesel. No federal rule requires it. States in the Northeast moved one by one, mostly through 500 ppm steps first:
| State | 15 ppm since | Rule and notes |
|---|---|---|
| New York | July 1, 2012 | ECL 19-0325: No. 2 heating oil for residential, commercial or industrial heating. The governor can suspend it during a supply shortage. |
| New Jersey | July 1, 2016 | NJDEP: 500 ppm from July 1, 2014, then 15 ppm for No. 2 and lighter fuel oil. |
| Connecticut | July 1, 2018 | Conn. Gen. Stat. 16a-21a: 500 ppm from July 2014 to June 2018, then 15 ppm. |
| Massachusetts | July 1, 2018 | 310 CMR 7.05: statewide distillate oil, 500 ppm from 2014, then 15 ppm. |
| Maine | July 1, 2018 | Maine DEP: 15 ppm for distillate fuel sold in the state. Fuel for manufacturing is exempt. |
| Vermont | July 1, 2018 | Moved with the rest of the Northeast. Vermont Business Magazine reported that the rest of New England, New York and New Jersey use the same 15 ppm standard. |
| Maryland | July 1, 2019 | COMAR 03.03.05.04: 500 ppm from July 2016, then 15 ppm. Fuel oil over 15 ppm must be dyed. |
Most of these rules let fuel already stored before the deadline be used up. Pennsylvania and states outside the Northeast aren't listed because we couldn't confirm a current 15 ppm heating oil rule from a state source.
15 ppm heating oil isn't automatically diesel. Heating oil that meets the sulfur limit still isn't certified for cetane or the other D975 properties, and it isn't designated as ULSD. If one tank feeds both a boiler and a generator, buy the fuel the engine needs.
BioheatBioheat: biodiesel blends in heating oil
Bioheat is a registered trademark for heating oil blended with biodiesel. It's licensed by Clean Fuels Alliance America, developed with the National Oilheat Research Alliance. Clean Fuels names the tiers by blend: Bioheat is B2–B5, Bioheat Plus is B6–B20, and Bioheat Super Plus is B21–B100. The B number is the percentage of biodiesel. ASTM D396 has covered B6–B20 heating oil blends as their own grade since an ASTM vote in December 2014.
| Where | Minimum blend in heating oil | Notes |
|---|---|---|
| New York State | B5 from July 1, 2022 · B10 from July 1, 2025 · B20 from July 1, 2030 | ECL 19-0327 (Chapter 750 of 2021). Applies to heating oil sold for use in any building. Kerosene is exempt. Sellers can't supply a blend that voids the burner or boiler warranty unless they warrant it in writing. |
| New York City | No. 2: B5 from Oct. 1, 2017 · B10 from Oct. 1, 2025 · B15 from 2030 · B20 from 2034. No. 4 and residual oil: B5 | Local Law 119 of 2016. Doesn't apply to fuel for emergency generators, or to a boiler fed from a dual-use tank that also supplies an emergency generator. Waivers exist for supply, price and boiler-warranty problems. |
| Connecticut | B5 from July 1, 2022 · B10 from July 1, 2025 · B15 2030 · B20 2034 · B50 2035 | Conn. Gen. Stat. 16a-21b, as a "low-carbon fuel blend." Subject to a waiver provision. |
| Rhode Island | B10 from July 1, 2023 · B20 from July 1, 2025 · B50 from July 1, 2030 | 2021 law (H 5132A) for No. 2 distillate heating oil. RI DEM lists B10 and B20 as current. A 2026 bill (S 2530) would push the later steps back. We couldn't confirm whether it passed. |
New York State's B20 date (2030) comes before New York City's (2034). The sources don't say how the two will line up, so ask your supplier what blend it delivers in the city.
Cold weather: biodiesel raises the cloud point. B20 clouds about 2–7°F higher than the No. 2 it's blended into, so outdoor tanks of Bioheat need the same winter planning as biodiesel blends. That's covered in biodiesel blends in winter. For the fuel itself (B100, D6751, renewable diesel), see R99 renewable diesel.
Dye & taxWhy heating oil is dyed, and how it's taxed
For federal excise tax, "diesel fuel" means any liquid that can run a diesel highway vehicle without further processing. IRS Publication 510 excludes only No. 5 and No. 6 fuel oil from that definition, so No. 1 and No. 2 heating oil count as diesel fuel. Under the federal rule (26 CFR 48.4082-1), diesel fuel can leave the terminal free of the 24.4¢ per gallon tax only if it's dyed with Solvent Red 164. That's why heating oil and off-road diesel are the same red. The dye shows which fuel is untaxed. It doesn't show what grade the fuel is. Details of the dye are in dyed vs clear diesel.
- Heating is a nontaxable use. Pub 510 lists home heating among the uses of undyed diesel fuel that don't count as highway use. The federal backup tax "doesn't apply to diesel fuel or kerosene used as heating oil or in stationary engines."
- Undyed heating oil exists. If the fuel was taxed at the terminal and then burned for heat, the tax can be claimed back. See off-road diesel tax refunds.
- States add their own taxes. State excise and sales tax on heating oil vary, and they're separate from state diesel tax. Our diesel taxes by state table covers on-road and dyed diesel only.
- Dyed fuel stays off the road. Red heating oil or red diesel in a highway vehicle is a taxable use. That's covered in off-road diesel compliance.
This section explains why the fuel is dyed and how it's generally taxed. Tax treatment depends on the fuel, the use and the state. Confirm with your state revenue agency or a tax professional before you rely on it.
Buying for a building with a boiler and a generator
Some sites, such as hospitals, offices and schools, have an oil-fired boiler and a diesel generator, sometimes fed from the same tank. New York City's Bioheat law even has a rule for that dual-use tank. Five questions keep the right fuel in the right place:
- What is the product designation? Heating oil, ULSD and 15 ppm nonroad diesel are separate designations under EPA's rules. The bill of lading or delivery ticket should name the product, because the color won't tell you (see how to read a fuel delivery ticket).
- Does the engine's tank get engine fuel? A generator needs nonroad diesel, 15 ppm with the cetane requirement. A dual-use tank should hold fuel that meets the engine's spec, since the boiler can usually burn it too.
- What's the sulfur and the bio blend? Ask for both in writing, especially in NY, NYC, CT and RI. Check that the blend is within what your burner maker approves.
- Is it ready for winter? For outdoor or aboveground tanks, ask for the cloud point. No. 2 heating oil can have a pour point as high as 20°F.
- How old is the fuel in the tank? Standby fuel sits. Test it before the season (see how long diesel lasts).
Diesel for your generators, equipment and tanks
FuelGo doesn't deliver heating oil or Bioheat. For a home or building oil tank, call a local heating oil dealer. What FuelGo delivers is dyed off-road and clear on-road diesel, plus R99 renewable diesel, nationwide. That's 20 to 4,400 gallons per drop and transport loads up to 7,500 gallons, into generator sub-base and day tanks, equipment and bulk storage tanks. Keep-full programs and remote tank monitoring keep standby tanks topped up without someone sticking the tank.
Not sure what's in an old tank? Lab fuel testing tells you, and fuel polishing, tank cleaning and fuel pump-out deal with what it finds. Dispatch runs 24/7/365 for emergency fuel. Get a free quote or call 800-720-4546. A dispatcher replies within the hour.
Common questionsHeating oil FAQ
What is heating oil?
Is heating oil the same as diesel?
Is heating oil the same as off-road (red) diesel?
Can you burn off-road diesel in an oil furnace or boiler?
Can you run a diesel generator on heating oil?
What is ultra-low sulfur heating oil (ULSHO)?
What is Bioheat fuel?
Why is heating oil dyed red?
Sources: 40 CFR 1090.80, definitions (heating oil, diesel fuel) · 40 CFR 1090.1015, fuel designations · 40 CFR 1090.305, ULSD standards · 40 CFR 60.4207, fuel for stationary diesel engines · EPA, nonroad, locomotive and marine diesel sulfur program · COMAR 03.03.05.04, No. 1 and No. 2 fuel oil (ASTM D396) · COMAR 03.03.05.02, No. 2-D diesel (ASTM D975) · Fuels Market News, ASTM adds B6–B20 grade to D396 (Dec. 2014) · EIA, British thermal units · EIA, use of heating oil · EIA, heating oil price definitions · EIA glossary, distillate fuel oil · IRS Publication 510, Excise Taxes · NY ECL 19-0325, heating oil sulfur · NY S3321-A / Chapter 750 of 2021, bioheating fuel · NYC Local Law 119 of 2016, clean heating oil · Conn. Gen. Stat. 16a-21a, heating oil sulfur · Conn. Gen. Stat. 16a-21b, low-carbon heating oil blend · Rhode Island H 5132A (2021) · Rhode Island DEM, Biodiesel Heating Oil Act · Rhode Island S 2530 (2026, proposed) · 310 CMR 7.05, Massachusetts fuel sulfur limits · Maine DEP, 15 ppm distillate transition letter · Vermont Business Magazine, ultra-low sulfur heating oil (July 3, 2018) · NJDEP news release 10-0086 (2010), heating oil sulfur rules · NJDEP Compliance Advisory 2012-15, heating oil in emergency generators · Clean Fuels Alliance America, Bioheat fuel trademark tiers (2022)