Photograph of a in-home oil tank - notice the small diameter vent line? Guide to Indoor Residential Heating Oil Storage Tanks
ASTs: Find & Fix Oil Tank Leaks & Other Problems

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Indoor oil storage tank inspection guide:

Advice and example photos for the visual inspection of above ground oil tanks for leaks and damage, improper piping, wrong location, bad fire clearances, including these details: damaged or leaky oil storage tanks, improper oil tank piping, valves, and indoor-type oil tanks located outdoors.

Here are photographs & explanation of some important indicators of oil storage tank condition that any home owner or home inspector can examine when an oil storage tank is visible and accessible inside or at a building.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

How to Inspect Indoor Oil Tanks

Inspection of the Oil Storage Tank Exterior

If an oil or other fuel storage tank is above ground and accessible for visual inspection it can and should be inspected for evidence of leaks or damage. Here are some inspection pointers for heating oil tanks.Is the tank exterior sound, without leaking seams or excessive rust?

Is there a patch or other evidence of a history of leaking?

[Click to enlarge any image]

In the photo at above-left, note the wet bottom of the tank? The inspector needs to decide if the oil on the tank exterior is from weeping at the fill or vent pipe fittings, from leaks at the oil line exiting the tank.

We were concerned about the evidence of seepage around the bottom left on this tank.

That oil stain does not seem to connect to the tank fill and vent fittings. The oil tank may have a perforation or an opening seam.

What about the next photo shown at left ? a leak at fuel line or at the Fire-o-Matic shutoff valve, or perhaps due to an actual tank perforation?

The size and wetness of the oil spill on this basement floor is a bit large to blame on a drippy fire safety valve.

But notice that in the upper portion of the photo the oil tank itself looks new. This oil spill was from the previous oil tank installed in this location.

Also look for water entry around the oil tank and don't confuse a water leak for an oil leak. Or more difficult, both leaks may be occurring at the same location. Look closely, and if necessary, touch, sniff, and sample the leak substance.

Leaky Oil Tanks That You Should Not Touch

This last photo shows an actual tank leaking at its bottom from a perforation.

Memorize this photo and look under oil tanks when you're inspecting above ground indoor oil storage tanks.

If you see a tarry "stalactite" drip formation on the bottom portion of an oil storage tank, the tank is leaking, has perforated, and can leak catastrophically at any moment.

Watch out: do not pick, poke, or even touch an oil tank that looks like this. T

he risk is that you perforate the already thin tank bottom, leading to a much bigger and more costly oil leak mess.


What are the Clearance Distances Required for Indoor Oil Storage Tanks?

Oil storage tank clearance distances requiredFor fire safety indoor oil storage tanks should not be located too close to oil burners or other heaters. Typical indoor clearance requirements specify that the oil storage tank should be 10 feet from the oil burner.

Note: the 2012 IRC changed this minimum indoor clearance distance to 5 feet between the oil burner and the oil storage tank. Update courtesy of Carson Dunlop Associates, Toronto. You can see this design in our sketch at left, provided courtesy of Carson Dunlop Associates.

Even before the 2012 IRC change, some communities permited the oil tank to be located closer, just 5 feet away from the nearest oil burner.

If you cannot meet this distance requirement your local building officials or fire officials may approve the oil tank installation if you provide a fire barrier between the oil tank and the burner.

Tanks should also be located where they will not be damaged, such as by being struck by a vehicle entering a garage.

In some communities indoor oil storage tanks located in a garage must be protected against possible vehicle damage by steel posts or similar means.

In some communities indoor oil storage tanks must also be secured against possibly falling or tipping over, such as by using angled steel piping set into the floor and ceiling or floor and wall around the oil tank.

Also see OIL BURNER INSPECTION & REPAIR for a discussion of the impace of leaks at the oil burner assembly itself.

Reader Question: what's the code on distance and clearance for metalbestos chimneys & vents vs oil storage tanks?

I am installing a pellet boiler and will need a second metal chimney as I am leaving my oil burner as a backup. I live in maine. The only place I would like the metal asbestos chimney would run 40” away from my oil tank. Do you know what the code is on this? I am having a heck of a time getting any answers regarding this? - R. B. Windham ME 2/27/2014


Insulated metal chimneys typically require a one-inch clearance from combustibles.

I think the reason you're not finding an answer to your question is that we're mixing up different constraints and safety concerns:

  1. The required separeation or clearance distances for flue vent connectors (generally single-wall uninsulated metal "flue pipes" or "stack pipes" that connect the heater to the chimney) - discussed
  2. The required separation of metal or insulated chimneys themselve from varous building components or combustibles - discussed
    for height above roofs,
  3. The required separation of heating appliances (like an oil burner) from heating oil storage (the oil tank) - discussed in this article (above) beginning at ABOVE GROUND OIL STORAGE TANK (AST) INSPECTION

If you were worrying about a horizontal distance for a flue vent connector, from a heater to the chimney, that'd be a different story. Suppose we wanted to run across an entire building from the heater to the chimney: the maximum horizontal length should not be more than 75% of the chimney height above the vent connector, or 100% if the chimney is insulated.

So you'd need a chimney at least 40 feet tall. But an option that may work acceptably is to include a draft inducer fan such as the type made by Field Controls.

Reader Comment: warning about improper oil storage tank support & code references

NHFireBear said:

We have found multiple situations where an owner has installed an AST supported by nothing more than a pile of wooden pallets or other combustibles (wooden structure, discarded tires, etc). NFPA 31 requires that above-ground tanks rest on solid concrete and that any supports be made of concrete, steel or solid masonry. Supports for outside tanks shall be fastened to their foundation.

Outside tanks up to 275 gallons may be installed within 5 ft of a property line and up to 660 may be installed within 10 ft, assuming local setback or fire code does not make it more restrictive than NFPA 31: 7.8 "Installation of Outside Aboveground Tanks."


Thanks NHFireBear - we've added your note. We appreciate the editing assistance. - Ed.


Continue reading at OIL FILL & VENT PIPING or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

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