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Posted: August 4, 2025
If you made the savvy move to have your heating oil tank filled this summer or spring, you might be wondering how long all that oil will keep, particularly when we’ve had such a hot summer. While we are all looking forward to some cooler weather, heating season feels like it’s a long way off. The good news is that the oil in your tank should be fine for at least 18 months or more.
That’s because heating oil, particularly ultra-low sulfur heating oil or Bioheat® fuel, has a relatively long shelf life. In most cases, heating oil stored properly in a clean tank can last as long as two years without any noticeable degradation. After that, chemical changes can begin to affect its quality.
In addition, when your heating oil tank sits empty, condensation can form—and that can result in all kinds of problems. That’s why a fill-up in the spring or early summer is such a great idea.
For starters, when condensation forms on the interior walls of an empty tank, that water drips down and sinks to the bottom of the tank (because water is denser than heating oil). That water becomes an ideal environment for bacteria and other microorganisms. Over time, it turns into sediment or sludge that can get into your fuel lines and clog them up. This will cause your heating system to shut down, probably next winter, when we’re in the middle of a deep freeze.
Sludge can also corrode your tank from the inside out—a big problem that could be difficult to see coming and costly to remediate. Be aware of the telltale signs that your heating oil tank is leaking—or could start soon.
The first sign your oil tank is leaking is a damp spot on the tank. Usually, they will appear on the underside of your tank or along the seam at the bottom of the tank. As the leak gets worse, oil will travel up the side of the tank.
If the leak goes undetected, black icicle-like deposits or sticky drips will form on the underside of the tank. You may or may not notice an oil smell. Reddish black spots may begin to appear on the floor underneath the area. Depending on how long the leak goes undetected, an oil stain will begin to develop on the floor.
In the winter, your tank doesn’t stay empty long, so these issues don’t come up. And, condensation is less likely to form in colder temps. But in summer, especially if your tank is outside, condensation will form quickly. Of course, if you’re signed up for automatic deliveries, we’ll make sure you’re topped off for the summer.
If your oil storage tank is very old, it may already be corroded inside. The oil in your tank can be contaminated by rust, water, dirt and debris, all of which can cause problems. Our residential Roth oil tanks systems are the best in the business. They are packed with features like insulation, self-venting, anti-freeze protection and filter systems that provide the ultimate convenience.
No matter what you need, the pros at Valiant are here for you, and we’re always happy to help. As a family-owned business, we’re your neighbors, and we care about our customers, so we go out of our way to exceed your expectations. Contact us today.