Are No. 1 Diesel and Kerosene the Same?

No—No. 1 diesel and kerosene are closely related but not the same. Both are light middle‑distillate fuels with similar cold-weather behavior, yet they are produced to different specifications, carry different additive packages and tax treatments, and are intended for different primary uses. In practice, some diesel operators blend kerosene with diesel in winter (where permitted) to improve cold flow, but straight kerosene generally lacks the lubricity and detergents modern diesel engines require.

What each fuel actually is

No. 1 diesel (also labeled No. 1-D, 1-D S15, or “winter diesel”) is a lighter diesel grade defined by ASTM D975 for compression-ignition engines. Kerosene (commonly “K-1” for heaters/lamps, and the basis for Jet-A in aviation) is defined by ASTM D3699. They come from overlapping fractions in the distillation column, which is why their properties can be similar, but they are finished differently for their intended uses.

How they compare

The following points outline the main ways No. 1 diesel and kerosene align. This helps explain why the two are often confused or even co-mingled for specific applications.

• Distillation range: Both are lighter than No. 2 diesel, with overlapping boiling ranges that favor easier cold starts and lower cloud/pour points.
• Cold-flow behavior: Both resist waxing and gelling better than No. 2 diesel, which is why they are used or blended in winter operations.
• Ignition quality: No. 1 diesel must meet a minimum cetane under ASTM D975 (typically 40+); kerosene’s ignition quality is usually similar but not controlled by a diesel engine standard.
• Sulfur levels: On-road No. 1 diesel in the U.S. must be ULSD (≤15 ppm sulfur). Kerosene is increasingly sold as “ultra-low-sulfur kerosene” (ULSK) at ≤15 ppm in many markets, though legacy higher-sulfur kerosene still exists for nonroad/space-heater use depending on local rules.
• Energy per gallon: Both have lower volumetric energy content than No. 2 diesel, leading to slightly reduced fuel economy or heat output versus standard diesel.

In short, they share a similar light profile and cold-weather strengths, and modern distribution systems may even originate them from the same base stock before different specifications and additives are applied.

Key differences that matter in the real world

Despite their similarities, several differences mean they are not interchangeable without care—and sometimes not at all, depending on equipment and regulations.

• Additives and lubricity: No. 1 diesel is additized to meet diesel-engine lubricity standards; kerosene typically is not. Straight kerosene can accelerate wear in modern high-pressure fuel systems unless a lubricity additive is used.
• Formulation intent: No. 1 diesel is built for engines (ASTM D975), including detergents and stability agents. Kerosene is intended for heaters/lamps (ASTM D3699) or aviation (Jet-A per ASTM D1655), not for over-the-road diesel engines.
• Regulatory/tax status: On-road No. 1 diesel is clear and taxed; off-road diesel and many kerosenes are dyed (often red) and untaxed for highway use. Using dyed fuel in on-road vehicles is illegal in many jurisdictions.
• Appliance compatibility: Heaters and lamps marked “K-1 only” should not be run on diesel (even No. 1) due to soot, odor, and wick fouling. Conversely, many modern diesel engines are not approved to run 100% kerosene.
• Emissions systems impact: Higher sulfur or non-diesel formulations can harm DPF/SCR aftertreatment and risk warranty issues. Always verify sulfur content and OEM approvals before blending.

These differences are why vendors may stock both products and why equipment manuals distinguish between them, even when the fuels look and pour alike.

Can you mix or substitute them?

If you’re considering using one in place of the other, the following checklist captures common, manufacturer-aligned practices and cautions. Always consult your equipment manual and local regulations first.

1. For diesel engines in cold weather: Many OEMs allow blending kerosene or No. 1 diesel into No. 2 diesel (often 10–50%) to improve cold flow. If using kerosene, add a lubricity additive meeting ASTM HFRR ≤520 μm and ensure sulfur ≤15 ppm for on-road vehicles.
2. Avoid 100% kerosene in modern engines: High-pressure common-rail systems rely on adequate lubricity and additive packages; running straight kerosene risks pump/injector wear and aftertreatment issues.
3. Prefer No. 1 diesel over kerosene for engines: Where available, a true No. 1-D S15 winter diesel already includes engine-appropriate additives and meets diesel specs.
4. Do not use diesel in kerosene heaters/lamps: Follow “K-1 only” guidance to prevent excessive smoke, odor, carbon deposits, and safety hazards.
5. Mind the dye and tax rules: Use clear, taxed fuel for highway vehicles; dyed kerosene or diesel is restricted to off-road or heating use in many regions.

Handled this way, you preserve reliability, compliance, and safety while still gaining the cold-weather benefits that make these light distillates attractive.

Why the labels sometimes get blurred

At fuel terminals, the same light distillate stream can be routed into different tanks and finished as No. 1 diesel or kerosene depending on which standard, additive package, dye, and tax category it’s assigned. This supply-chain reality explains why some retail pumps loosely refer to “kerosene” when they may in fact be selling a 1-D product—or vice versa. The only reliable identifiers are the posted product spec (ASTM standard), sulfur level, and dye/tax status.

Bottom line

No. 1 diesel and kerosene are not the same, even though they’re closely related and sometimes blended. Use No. 1 diesel for engines where available; if kerosene is blended for winter operation, follow the manufacturer’s limits, add lubricity, and ensure ULSD-equivalent sulfur for on-road use. For heaters and lamps, stick with K‑1 kerosene as specified.

Summary

No. 1 diesel (ASTM D975) and kerosene (ASTM D3699) are light, cold-friendly fuels with overlapping properties, but they differ in specifications, additives, legal status, and intended uses. They are not interchangeable by default: diesel engines generally require additized No. 1 diesel or carefully limited kerosene blends with added lubricity, while kerosene appliances should use K-1 only. Observing the correct fuel, sulfur content, and regulations preserves equipment life, emissions compliance, and safety.

Can I use number 1 diesel in a kerosene heater?

Yes, you can generally burn #1 diesel in most kerosene heaters. The fuel is very similar. Add 3oz of isopropyl alcohol to each gallon of diesel to reduce the increased wear on your wick and you’ll be just fine. I burn diesel in this heater because I cannot find kerosene.

Is number 1 fuel oil the same as kerosene?

Many similarities can be expected between kerosene and #1 fuel oil. After all, kerosene is a derivative of #1 fuel oil. Some of their differences are that Number 1 fuel oil is a little heavier, has more impurities, and has a higher viscosity. This is because this fuel oil has less processing time.

Can I use kerosene instead of diesel?

Technically, you can put kerosene in a diesel engine, but doing so is not recommended, and it can lead to serious engine issues. Diesel fuel has higher lubricity than kerosene, which helps lubricate the fuel system, including the injectors, pumps, and other components.

Is diesel #1 the same as kerosene?

Diesel (usually #2 diesel) is a heavier fuel with more energy content than kerosene (#1 diesel), but kerosene is lighter, more volatile, and offers better cold-weather performance. Diesel contains engine additives, whereas kerosene is a purer fuel, and while kerosene is often blended with diesel to improve its cold flow, using kerosene alone in a diesel engine is generally not recommended due to potential damage and liability.
 
Key Differences

• Refining & Purity: Kerosene is a more refined, pure fuel with fewer additives than diesel fuel, which contains additives for engine performance and handling. 
• Energy Content: Diesel fuel has a higher energy (BTU) content per gallon compared to kerosene. 
• Volatility & Cold Weather: Kerosene is a lighter fuel, meaning it has a lower cloud point and is less likely to solidify in cold temperatures, making it more suitable for winter conditions. 
• Usage: Kerosene is often used in kerosene heaters and as a component in Jet-A fuel. Diesel fuel is used in transportation, generators, and other industrial applications. 

Interchangeability & Blending

• Kerosene in Diesel: Opens in new tabKerosene can be burned in a diesel engine, but it’s not recommended for routine use. The lack of diesel additives can cause issues, potentially leading to engine damage. 
• Diesel in Kerosene Heaters: Opens in new tabDiesel can be used in a kerosene heater, but it burns less cleanly and efficiently, producing more fumes and potentially leading to damage over time. 
• Winter Blends: Opens in new tabIn colder climates, kerosene (#1 diesel) is often blended with #2 diesel fuel (typically 80/20, 70/30, etc.) to improve the cold flow properties of the diesel fuel and prevent gelling. 

When to Use Each

• Use Kerosene: Opens in new tabFor kerosene heaters, or as an additive to diesel fuel during extreme cold to prevent gelling. 
• Use Diesel: Opens in new tabFor diesel engines, generators, and transportation applications where its higher energy content is beneficial.