Homeowner’s Guide to Residential Oil Tanks

David Sherwood Sherwood Inspection Services, LLC Leave a Comment

residential oil tank

We often get various questions from our customers about their oil tanks, so we put together a list of frequently asked questions along with answers from our experts on residential oil tanks. We hope it will help you get to know your oil tank better and avoid major costs in the future.


How costly can an oil tank spill be?

It can be tens of thousands of dollars or more. 

How long does an oil tank last?

Experts agree that under ordinary circumstances the reliable lifetime of a typical single-wall oil tank (the familiar oval shape) is about twenty years. Some tanks might last much longer, and some will be in dangerous disrepair sooner. It’s crucial information for you to learn more about the lifespan of your home’s oil tank.

But how do you know the age of the tank in the home you’re interested in purchasing? And how do you know that circumstances have been favorable to assure a long, reliable tank life?

Newer tanks often have a data sticker affixed to the surface. It generally includes the manufacturer’s name, the tank capacity, the tank steel gauge (thickness), and the manufacture month and year, among other things. Older tanks have some of these data stamped onto a metal plate affixed to the surface. Unfortunately, the stamped plates are often illegible – particularly if the tank had been repainted by a well-meaning homeowner, as is often the case—and the stamped plates seldom include the manufacture year!

What do we mean by “favorable circumstances” for long tank life? Or more to the point, what are some yellow flags that suggest unfavorable conditions?

Oil storage tanks are made of steel. Steel is vulnerable to corrosion – that’s rust. Think of what causes your car to rust, and where it’s most prone to rust: exposure to salt and exposure to water, particularly on unpainted surfaces and surfaces that aren’t exposed to moving air and that are likely to stay moist. Oil tanks in homes near the shore typically have a shorter life from the corrosive effects of the lovely salt air that makes you want to own a home close to the shore! Oil tanks that are installed within a couple of inches of the foundation wall are prone to failure on the surfaces we can’t see that are against those walls. This is due to condensation trapped between the foundation wall and the tank. Oil tanks that have been dented, scraped, or scratched are less reliable. There is no patch or repair to the surface of a tank that is reliable. Most of these things can be seen with the naked eye or anticipated on the basis of the tank’s location.

But here’s the wildcard: The part of an oil storage tank most vulnerable to corrosion is the part that’s truly impossible to see: the interior. And the chief corrosive agent is the one you can’t know about: water (and sometimes other contaminants) in the oil that’s been delivered to your tank since the day it was installed!

Water is nearly always present as a contaminant in heating oil, for example, from condensation or leakage in wholesalers’ or suppliers’ tanks. Oil and water don’t mix, and water is heavier than oil. Water settles to the bottom of an oil tank. Many older tanks have the supply line to your oil-burning appliance exiting the tank through a fitting on the side of the tank. The fitting is installed an inch or two above the belly of the tank. This traps a pool of water and contaminants on the bottom of the tank – not a great design! Similarly, tanks with a supply line exiting the top of the tank leave a pool of contaminants below the level to which the supply line is installed inside the tank. A tank can look perfectly fine on the exterior but can be dangerously undermined by corrosion on the interior! Even a tank with a supply line exiting on the bottom – more or less standard on newer tanks – can have a pool of water and contaminants in the belly if it is pitched (tilted) improperly.

So what assurance can a home buyer have that an oil storage tank is ok?

Sherwood Inspection Services provides an ultrasonic oil tank inspection service. This method of oil tank testing allows us to determine the thickness of the tank belly – the part of the tank that is most vulnerable to corrosion. We develop a report to show you the thinnest measure and its location. If the tank belly’s measures are within a certain range of the control measure, the tank will qualify for the TankSure™️ Program. If you oil supplies takes part in the program, your tank will be insured for $1,000 for the coming year, which is typically enough to replace the tank in case of failure.

What if the tank does not qualify for TankSure™ due to a low ultrasonic reading, or if the tank is obviously leaking or damaged on the basis of a visual inspection? Is the cost of a Sherwood TankSure™ inspection justified in that case?

Clients and agents agree that the low cost of a TankSure™ inspection is worthwhile – even if the tank does not qualify for the program – because the program provides buyers with the negotiating leverage of an industry-recognized standard in the event of the presence of a non-qualifying oil storage tank. The small investment in the TankSure™ inspection is often returned ten- or twenty-fold at the closing table!

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