Photograph of a residential outdoor above ground oil tank - was this tank intended for outdoor use? Photo courtesy Arlene Puentes, Kingston NY Guide to Above Ground Outdoor Home Heating Oil Storage Tanks

  • ABOVE GROUND OUTDOOR OIL TANKS - CONTENTS: Above ground outside oil tanks: installation, codes, inspections, leaks, troubleshooting, Heating oil additives and chemicals for outdoor oil tanks to deal with water, icing, and waxing in outdoor oil storage tanks
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Above ground heating oil storage tank - AST inspections outdoors:

How to inspect above ground oil storage tanks (ASTs) when they are installed above ground outdoors.

This article discusses aboveground outdoor oil storage tank installation, clearance distances, codes, standards, and inspection.

We describe the risks of heat loss or leaks when above-ground outdoor oil storage tanks are used outside. This article series aslo explains how water gets into oil storage tanks no matter where they are located, above ground oil tanks, buried oil tanks, or even possibly indoor oil tanks. Photograph at page top courtesy of Arlene Puentes.

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Codes, Installation, Inspection of Above Ground Oil Storage Tanks Installed Outdoors

Aboveground outdoor oil tank (C) Carson Dunlop AssociatesThe article also discusses the problems faced by owners of above ground oil storage tanks located in cold climates. This article is a sub-chapter of OIL TANK INSPECTIONS

[Click to enlarge any image]

This article, sketchs, and photographs give advice and example photos for the visual inspection of above ground oil tanks for leaks and damage including damaged or leaky oil storage tanks, improper oil tank piping, valves, and indoor-type oil tanks located outdoors.

Sketch of an above ground outdoor oil storage tank is courtesy of Carson Dunlop Associates.

Article Contents

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

Above Ground Oil Tank Location & Clearance Distances

Question: AST required clearance distance from windows

2017/11/26 Jerry said:

I am installing an outside oil tank. Can I install it between 2 windows. 1 foot from each window?

Reply: AST must be 5 ft. from buildings, vents must be at least 2 ft. from openings.


The short answer is no. You need no less than two feet from a window and you may need to be five feet from the building wall, giving a still greater distance.

For example the 2008 UMC (cited below) states [excerpting]

1305.13.4 Above ground; outside a building. Tanks located above ground, outside of buildings, shall comply with the following requirements:

2. Distances to buildings, lot lines and other tanks.

Storage tanks of a capacity greater than 330 gallons (1250 L) shall be not less than 1 1/4 tank diameters and in no case less than 10 feet (3048 mm) from the tax lot line, the nearest building or adjacent tank.

However, in no case shall the clearance between individual tanks and the tax lot line be less than the distance fixed by the following formula:‡

M.C. = 10 + 4 [ (G-275) / 5000 ] (Equation 13-1)

where: M.C. = Minimum clearance from nearest surface of tank to tax lot line, in feet. G =Capacity of tank, in gallons.

1305.7.2 Termination location.

The location of the normal vent pipe terminations shall comply with the following:

1. Liquid fuel normal vent pipes shall terminate outside of buildings in a nonhazardous location at a point not less than 2 feet (610 mm) measured vertically or horizontally from any building opening and not less than 2 feet (610 mm) nor more than 12 feet (3658 mm) above the fill pipe terminal.

2. If the normal vent pipe terminal is not visible from the fill pipe terminal location, a 1-inch (25 mm) tell-tale line shall be connected to the tank and shall parallel the fill pipe and terminate at the fill pipe terminal with an unthreaded end. Such tell-tale lines shall be provided with a check valve set to prevent flow of surface water to the storage tank.

3. Normal vent pipes shall terminate sufficiently above the ground to avoid being obstructed with snow or ice.

4. Normal vent pipes from tanks containing heaters shall be extended to a location where oil vapors discharging from the normal vent will be readily diffused.

Clearance Distances for Oil Tanks from Building Walls, Foundations, Property Lines

NFPA 30 Table Reference Table (NFPA 30 2008) gives the clearance distances for an above ground oil storage tank (AST) to property lines and buildings. A 275 gallon oil tank needs to be 5 ft. or more from any "important building". That specification would include the distance to a window as that's a component of your building.

In addition, the Uniform Mechanical Code, such as adopted by New York City and many other municipalities (2008) specifies that no oil storage tank can be closer than three feet from a building foundation.

Typical Heating Oil Storage Tank Clearance Distances Required for AST's:

NFPA 30 Table (b) Clearance Distances for Aboveground Oil Tanks

Tank Capacity, Gals Property Line, Ft. Important Bldg or Public Way, Ft Notes
< 275 5 5  
275 - 750 10 5  
751 - 12,000 15 5  


In the same document, NFPA 30 Table (1) gives adjustments to these distances to the property line and to important buildings for tanks of various types

Source: NFPA 30-2008: Basic Requirements for Storage Tanks UL-142 Steel Aboveground Tanks for Flammable & Combustible Liquids [PDF - workbook] New York City Metro Chapter
Society of Fire Protection Engineers New York, NY — February 22, 2011 , retrieved 2017/11/26, original source:


Clearance Distances for Heating Oil Storage Tank Fill & Vent Piping

I have not found an oil storage tank clearance distance citation that specifically addresses windows. I agree with the implication of your question that during oil storage tank filling the venting of heating oil fumes from the tank vent might produce undesirable odors that could enter a building through a nearby window.

Heating oil is considered a Class II flammable liquid. For more-volatile Class I liquids, more stringent requirements are given for clearance distances from vent piping to building openings.

Codes & Standards for Aboveground Oil Tank & Tank Piping Clearance Distances

Indoor vs Outdoor Use Rating for Above Ground Oil Storage Tanks

Oil tank label tag

Oil Tank Size and Rating for indoor use but Used Outdoors: If you find a 250g or 275g oil storage tank above ground outside, check its label and UL rating to see if that location was permitted.

Similarly, if you learn that a buried oil tank is an older, small-capacity tank such as 250g or 275g, it is reasonable to assume that an "indoor use only" oil storage tank was buried outside, as we have not located a single instance of a 20 year old 250/275 gallon oil storage tank which was tested, UL-Labeled, and rated for outdoor use above ground nor underground.

An oil tank lacking a rating for outdoor or buried use may lack adequate corrosion resistance and strength, risking rust-through, leaks, and even a dangerous collapse hazard.


See OIL TANK STANDARDS - UL for more about UL labeling & standards for heating oilstorage tanks.

Oil tank label

Such oil tanks often need to be replaced. Unfortunately so many indoor oil tanks have been used outside, above ground or buried, that their use has been so popular that UL standards for labeling and controlling oil tank use are a bit more confusing.

Modern oil tank labels might no longer indicate if the tank is intended for outdoor use or not, and modern oil tank manufacturers may have rated tanks which were previously labeled "indoors" as now suitable for outdoor use or even buried-use.

Check with the manufacturer of your oil tank before moving it, using it outdoors, or burying it.

Problems Faced by Above Ground Outdoor Oil Storage Tanks

Photograph of an open oil outdoor oil tank vent and an oil tank filler pipe exposed to roof spillage.How Water Gets Into Oil Storage Tanks

Water can enter an oil storage tank by more than one means:

Problems Caused When Water Enters an Oil Storage Tank?

Photograph of a half buried outdoor oil tank. Was this oil tank intended for this exposure? Was it intended for ground contact.

What happens when an oil tank is outdoors? Water can enter the oil storage tank where it causes possibly serious problems for the heating equipment.

Water in the fuel oil or simple exposure of the oil to cold temperatures can lead to loss of heat and resultant damage to a building by several means:

The photo shows an oil tank which is half buried outdoors under a deck. Was this tank intended for outdoor use at all? If so, was it intended for use when in contact with the ground? Probably not. The risk is tank rusting, water entry, oil leaks, and related problems we've already listed.

Photograph of a dual use outdoor oil tank with leaks at the oil lines.

Outdoor oil tanks in cold climates risk loss of heat from freezing water or jelling fuel as we just cited. In the photo shown here the oil lines are taken off of the top of the oil tank so as to avoid picking up water that may be present in the tank, avoiding the icing problem.

Note that no heat tapes are in use on the oil lines (good, that reduces a fire risk). It looks as if there has been some seepage around these oil lines, that the tank is old, and that one tank is being used to serve two oil-fired devices (two sets of oil lines leaving the tank).

Water in oil tanks also often leads to internal corrosion and leaks in the tank itself, regardless of the tank location, though buried tanks and indoor oil tanks are less prone to water accumulation due to in-tank condensation in response to temperature changes than a tank located above ground outside.

Oil storage tanks usually fail from rust perforation due to combination of water inside the tank with sulphur in the fuel oil. External rust, unless very heavy, isn't highly correlated with internal rust. A new tank, when required, may cost more $2000. installed, including removal of the old oil tank.

When an outdoor tank is exposed to these conditions and even for an indoor tank which we suspect has had a dose of water and sludge, we recommend regular use of a fuel oil additive such as 4 in 1 Hot(TM) to absorb water and to help break up sludge. The best solution is to locate the tank indoors or to build a heated shelter over the outdoor tank.

Heating or Fuel Oil Additives for Outdoor Oil Tanks

In cold climates, heating or fuel oil additives for above-ground outdoor oil tanks can help prevent loss of heat by adding a pour point depressant which lowers the temperature at which the heating oil will form waxes or jell, and by adding a chemical, typically an alcohol, to remove [small amounts] of water from the oil.

I've used a product called "4-in-One Hot" which contains both a sludge break-up chemical and alcohol to help remove water from the heating oil. Such additives may indeed help break up sludge which tends to clog old heating oil lines.

See HEATING OIL CLOUD WAX GEL POINT for details about heating oil waxing or jelling

Watch out: two warnings about using heating oil additives and chemicals for outdoor oil tanks:

  1. No oil additive is going to remove a large quantity of water from an oil tank. Measure the amount of water present. If it's inches, your oil company can pump the water out (leaving the heating oil intact).

  2. Oil additives that break up sludge might in some circumstances precipitate frequent clogging of the oil filter installed at your heating boiler or furnace since an increased amount of debris is being freed and sent along the oil lines.

    If you find that your boiler stops working shortly after receiving an oil delivery, check to see if the problem was a clogged oil filter. That would suggest that your tank has a lot of debris and that the debris or sludge were being stirred up whenever oil was delivered. Discuss this concern with your heating service contractor.

Pour point depressants for heating oil tanks are about the same as similar products used by owners of diesel fuel powered automobiles and trucks in cold climates, but except in dire emergency I would not recommend substituting one for the other as there are some differences in these fuels and chemicals.

Note: these tips are not a complete oil tank installation guide. Proper installation must be done by trained service technicians and must comply with local building codes.

Readers whose heating system uses an above-ground outdoor oil storage tank should be sure to also read HEATING OIL CLOUD WAX GEL POINT


Details about the various types of oil storage tank additives, treatments & chemicals and some warnings about their use are at OIL TANK TREATMENTS.


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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