Have you ever wondered if the furnace oil used to heat your home is the same as the diesel fuel that powers your car?
While both might seem similar at a glance, understanding their differences is crucial for safe and efficient use.
Imagine you’re about to refill your home heating system; knowing exactly what type of fuel to use can save you from a costly mistake.
So, is furnace oil diesel?
This article will jump into the specifics of furnace oil and diesel, highlighting their unique properties and applications.
You’ll discover not only the chemical distinctions but also practical tips on their respective uses.
By the end of this read, you’ll be well-equipped to make informed decisions about fuel usage in your daily life, ensuring safety and optimizing performance.
Is Furnace Oil Diesel or Not?

Many people wonder, is furnace oil diesel or not?
Although both come from crude oil and appear similar, they have unique properties and specific uses.
Understanding the differences between furnace oil and diesel is key to ensuring you choose the right fuel for your home heating system or equipment.
Let’s dive into the distinctions to help you make informed decisions about fuel usage.
What Is Furnace Oil?
Furnace oil, often referred to as heating oil, serves as a primary heat source in many homes and buildings, especially in colder regions.
Typically derived from the distillation of petroleum, this oil is heavier than diesel fuel.
Your furnace oil might be used in boilers or furnaces for generating heat through a combustion process.
The main characteristics of furnace oil include its high boiling point and its ability to generate a significant amount of heat, making it highly effective for warming larger spaces.
But, it contains more impurities compared to diesel, which impacts its efficiency and combustion quality.
What Is Diesel?

Diesel, on the other hand, is a light-duty fuel primarily used in engines designed for cars, trucks, and some types of machinery.
Originating from the same crude oil as furnace oil, it undergoes a different refining process that strips away more impurities, enhancing its combustion efficiency.
Diesel’s most critical property is its cetane number, which indicates how quickly and efficiently the fuel burns.
High cetane numbers lead to better engine performance with reduced emissions. Also, diesel contains additives that improve its stability and combustibility, ensuring engines run smoother and last longer.
There’s often confusion about whether furnace oil and diesel are interchangeable, as they originate from the same raw product.
However, their formulation and intended use differ significantly, affecting their performance and suitability for specific applications.
It’s crucial to use each product as intended to ensure optimal performance and safety.
Differences Between Furnace Oil & Diesel
Wondering is furnace oil diesel? If so, understanding the differences between these oil types will help with using them effectively and safely.
Here’s what sets them apart:
1. Chemical Composition and Physical Properties
Furnace oil and diesel differ primarily in their chemical composition and physical properties.
Furnace oil, also known as heating oil, is a heavier fuel compared to diesel.
It has a higher viscosity, meaning it’s thicker.
This quality makes it less volatile and suitable for stable, slow-burning applications, like heating your home.
On the other hand, diesel is lighter and designed for the high-combustion environments of engines.
Diesel’s lower viscosity allows for finer atomization in combustion, which is essential for the operation of diesel engines found in cars, trucks, and heavy machinery.
2. Sulfur Content and Environmental Impact
Another key difference lies in their sulfur content.
Typically, furnace oil contains higher levels of sulfur compared to diesel.
High sulfur content can lead to more emissions when burned, which can be harmful to the environment.
Recent regulations require diesel to be ultra-low in sulfur to reduce emissions, making it a cleaner-burning option than traditional furnace oil.
For instance, ultra-low sulfur diesel (ULSD) contains only 15 parts per million (ppm) of sulfur.
3. Applications and Use Cases
Your choice between these fuels should align with their intended applications.
Furnace oil, given its properties, is ideal for heating systems. It’s commonly used in residential boilers and furnaces to keep homes warm during colder months.
Conversely, diesel powers a wide range of vehicles and equipment. Its efficient combustion properties make it the preferred fuel for transportation and heavy-duty machinery.
Using furnace oil instead of diesel in an engine may lead to inadequate combustion and damage due to its heavier and oilier nature.
4. Performance Considerations
Performance factors are crucial when selecting your fuel type.
Diesel engines, for instance, are engineered to maximize the fuel’s combustibility.
They rely on diesel’s specific attributes for optimal efficiency and longevity.
In contrast, using diesel in a system designed for furnace oil could result in overheating and system inefficiency due to diesel’s higher combustibility and different burn rates.
Recognizing these distinctions ensures you use each fuel type as intended, optimizing performance and safeguarding equipment.
Whether heating your home or fueling vehicles, choosing the correct type of oil makes a significant difference in functionality and environmental impact.
Can You Put Diesel in an Oil Furnace Tank?
Yes, you can use diesel in an oil furnace tank, though it’s important to know why and how this works without causing damage or inefficiencies.
Diesel and home heating oil, commonly referred to as furnace oil, share enough similarities because both derive from petroleum.
This interchangeability occurs because both fuels are middle distillates of crude oil, placing diesel as a suitable temporary substitute for heating oil in emergencies.
But, you should consider a few critical factors before pouring diesel into your furnace tank.
Diesel is generally more expensive than heating oil due to higher road taxes levied on diesel.
Using diesel for a prolonged period could lead to higher operational costs.
Also, diesel contains a lower sulfur content compared to traditional furnace oil.
While this is better for the environment, it may impact the operation of older furnace systems designed specifically for higher sulfur content.
If your heating oil supply runs low unexpectedly, adding diesel to your furnace oil tank can keep your system running until you can replenish your heating oil.
To do this efficiently, ensure you follow these steps:
- Purchase Diesel: Visit a local gas station and purchase enough diesel to meet your immediate needs. Typically, a few gallons will suffice until you acquire more heating oil.
- Add to Tank: Pour the diesel directly into your furnace oil tank. If possible, mix with the remaining heating oil to ensure smoother operation.
- Restart System: Once you’ve added the diesel, restart your furnace system. It should operate normally with diesel as the fuel source.
These steps ensure that you don’t misuse diesel or inadvertently damage your heating system.
Is Furnace Oil Diesel? Or Are They Entirely Different?
So, for all of you wondering: ” Is furnace oil diesel?” – while they share some similarities, it’s crucial to recognize that they are not the same.
Each has specific uses and characteristics that make them suitable for particular applications.
If you’re considering using diesel as a substitute for heating oil in an emergency, remember this should not be a permanent solution.
If you’re low on furnace oil, it might be better to order a new supply online than to mess with using diesel as you risk potential furnace damage.
How can you get a furnace oil delivery quickly? Simply contact us or order oil online!
We offer same-day furnace oil deliveries right to your doorstep for maximum convenience.