December 10, 2022
Furnace Installation in San Antonio, TX

Furnace Oil: Does It Go Bad and After How Long?

Furnace oil is a volatile fluid that fuels furnaces in homes and commercial buildings. It is made up of a mix of hydrocarbons, oxygenates, and other types of chemicals that burn to create heat. If you use furnace oil in your home, you may wonder how long it lasts and how to tell when it is time to replace or refill the oil. Or let’s assume winter has just ended and you still have some furnace oil left in the tank. Will it be safe to burn this oil next winter?

How Long Does Furnace Oil Last?

Furnace oil can last for a period of 18 to 24 months. That is because furnace oil tends to break down over time, becoming thinner and less effective as a source of heat. Please note that furnace oil will last for that long only if effective additives are mixed with it upon delivery. No. 2 heating oil, which is the most common type of furnace oil, is typically the same as diesel oil. The only difference is that diesel has more additives in order to boost its effectiveness in the motor industry. That means this variety of furnace oil will last as long as diesel oil.

Issues That Have an Impact

There are various factors that contribute to the life span of furnace oil. Let’s consider some of them.

1. The Kind of Furnace

The hotter the furnace, the faster the oil will evaporate. Furnaces with low BTUs will burn the same amount of oil over a longer period as compared to those with high BTUs.

2. The Quality of the Oil

Furnace oil should come from a reputable manufacturer. This is the only way to ensure that it will work as expected. Anything that is of high quality tends to last longer than anything of low quality.

3. The Environment of the Home

The environment of the home has an effect on how long the oil lasts. The temperature and humidity also play a role in how long the oil lasts. For example, if you live in a humid environment, the oil can last longer than if it were located in a dry one.

4. Condition of the Storage Tank

The condition of the tank also has an effect on how long the oil lasts. Make sure you inspect it regularly to detect any cracks or leaks that may cause the oil to leak out faster than anticipated. Please also note that if moisture finds its way into the tank, the oil may break down faster than expected.

5. How the Oil Is Used

The way the oil is used also affects how long the oil lasts. When the oil is burned at a high temperature, its life span will be shorter than if it were turned down or on low. When oil is burned continuously, its life span tends to be shorter than when it is used intermittently.

6. The Size of Your Home

The size of your home also has an effect on how long the oil lasts. A larger home will use more oil than a smaller one to meet the same temperature requirement. For example, a two-bedroom or a one-story house will use approximately half the amount of heating oil that a five-bedroom or a two-story house will use.

7. The Design of Your Home

The design of your home can also affect the consumption of the oil. For example, a house with a vaulted ceiling will use less oil than one with an open design. The nature of the walls also has an effect; thick or insulated walls can conserve heat better than thinner ones. If there are empty cavities between your plasterboards and the exterior walls, then your house is prone to much heat loss, and this will require more oil to keep the house warm.

How to Tell If Furnace Oil Has Expired

There are various indications that furnace oil has passed its period of usefulness. Here are some of them.

Low Efficiency

This is one of the most common signs. If you are unable to achieve the desired amount of heat from the furnace, chances are that the oil has expired. Your furnace could even shut down completely. This is because it requires a certain amount of heat for it to function properly.

The Smell of the Oil

If the furnace oil in your tank has expired, the smell will be more pronounced than usual. It may not smell a specific way, but it will smell like something unpleasant. This is usually because of the by-products of oil degradation, which include asphalt and tar. When you notice the smell, you should contact a professional immediately to repair it.

The Sound of the Furnace

The sound of the furnace may also change if the oil has expired. If it is rattling or shaking more than usual, that could be a sign the oil has broken down and is affecting your furnace. Please note that this doesn’t necessarily mean that the oil has expired. You should consult a professional before you draw any conclusions.

Dealing With Expired Oil

You may wonder if products added later can extend the life span of your furnace oil. As already discussed, for the oil to last longer, supplements should be added upon delivery. You should communicate with your supplier to ensure that these additives are present in the oil. Mixing additives after the delivery date would not extend the life span of your furnace oil.

If you suspect that your heating oil has expired, you should contact a professional to analyze the situation. If the oil is expired, they will help you empty the tank, clean it, and refill it with fresh heating oil. This can be done at any time of the year, but there are certain times when it is more convenient in terms of service availability and savings. These periods include the following.


During summer, you can take advantage of the fact that most homeowners don’t think about furnace oil because it is warm outside. For that reason, heating oil companies lower their prices.

Before the Holidays

During Christmas and Thanksgiving, the weather is usually cold. For that reason, oil prices go up. Suppliers also tend to charge higher delivery fees. You should therefore stock up on furnace oil before these holidays begin.

During Spring

Reports indicate that homeowners use more heating oil between October and February than at any other time. This means that you will be paying higher delivery fees and prices at this time of the year. To save money, you should buy furnace oil during springtime, when oil companies offer special discounts and deals.

On Weekdays

If you are unlucky and your heating oil runs out in the middle of winter or fall, you should try to buy your furnace oil on weekdays. This is because weekdays are the normal working days for most people, and most suppliers tend to charge lower delivery fees. You should also remember to time your delivery to normal working hours.

At Beyer Air Conditioning & Heating, we are dedicated to providing our customers with the best possible heating oil at the most affordable rates. If you are looking for a heating oil delivery service in San Antonio or the surrounding area, get in touch with our representatives, and we will do everything possible to help you.

We also provide comprehensive heating maintenance, installation, and repair, and we do the same for cooling and indoor air quality equipment. In addition, we handle air duct cleaning and repair and perform sheet metal work.

Call us at Beyer Air Conditioning & Heating to discuss your situation or schedule an appointment.

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