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Guide to Above Ground Outdoor Home Heating Oil Storage Tanks
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InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.
AST inspections outdoors: How to inspect above ground oil storage tanks (ASTs) when they are installed above ground outdoors: This article discusses the risks of heat loss or leaks when above-ground outdoor oil storage tanks are used outside. It 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.
Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman.
Guide to Issues with Indoor-rated Oil Storage Tanks Used Outdoors
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 The article explains the problems caused by water in oil tanks and also 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
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.
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. Readers whose heating system uses an above-ground outdoor oil storage tank should be sure to also read HEATING OIL CLOUD WAX GEL POINT and OIL TANK SLUDGE.
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 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.
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 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.
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Problems Faced by Above Ground Outdoor Oil Storage Tanks
How Water Gets Into Oil Storage Tanks
Water can enter an oil storage tank by more than one means:
- Water may collect in an oil storage tank, above ground or buried, or in some cases even indoors, when the oil is left at low levels
in the tank for long periods, particularly in periods of cool weather or in periods of alternating warm humid and then cool weather. As
temperatures change around and then in the oil tank, warm moist outside air is drawn into the oil storage tank through its vent. Moisture
in the air condenses on the cool tank interior surface, and can accumulate in the tank.
- Water may enter an oil delivery truck by the same means as just discussed above for oil tanks. From the oil delivery truck
water, along with oil, may then be pumped into the property owners oil storage tank. Some oil companies are quite diligent to
avoid these problems or to include water filters on their delivery trucks.
- Water may enter an oil storage tank by delivery of a "bad" batch of oil from the oil delivery company. Those huge commercial
oil storage depot tanks you may see, perhaps near a railroad line or a river, may be deliberately maintained with a few feet of water
in the bottom of the tank so that if a leak occurs it can be discovered as escaping water before the actual oil leaks out.
When an oil
company truck is being filled from one of these tanks, in some conditions some of the larger tank's water can enter the oil delivery
truck tank where under some circumstances it can also be pumped into the homeowner's oil tank.
- Water may enter an outdoor oil storage tank from roof runoff (rain or melting snow) spillage onto or near the oil filler or vent
line for an oil tank. I've seen this condition both at above ground tanks which were placed under the house eaves (right where roof
spillage fell onto the tank) and also at buried tanks whose filler pipe was set flush with the ground.
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Problems Caused When Water Enters an Oil Storage Tank?
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.
- In cold climates, water in the oil tank, which will reside at the bottom of the tank, may freeze in the tank
or in the oil line, particularly for installations at which the oil line is attached to the
bottom of the tank.
- In warm, moderate, or cold climates water in the oil storage tank can cause rusting which is pulled into the heating equipment where it clogs the filter, fuel pump, or
oil burner nozzle
- In some modern high efficiency systems a special filter is used which will stop flow completely (such as the "System 2000" heating boiler), shutting
down the burner in response to water or debris buildup in the filter - a move to protect the equipment.
- In cold climates, heating oil in an outside oil tank supply line may "Jell" and stop flowing at cold temperatures.
- Fire risk: Outside above ground oil storage tanks in cold climates exposed to jelling of the heating fuel may be (in error) fitted with
a heating tape in an attempt to avoid freeze-up in the oil line itself. This is a potential fire hazard.
Heat tapes should not be used on heating oil lines.
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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.
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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.
But I'd cite two warnings about using heating oil additives and chemicals for outdoor oil tanks:
- 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).
- 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.
See HEATING OIL CLOUD WAX GEL POINT for details about heating oil waxing or jelling.
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Technical Reviewers & References
Related Topics, found near the top of this page suggest articles closely related to this one.
- Arlene Puentes, an ASHI home inspector in Kingston, NY, contributed the example photograph of an outdoor aboveground oil tank. Ms. Puentes can be contacted at ap@octoberhome.com
- Mark Cramer Inspection Services Mark Cramer, Tampa Florida, Mr. Cramer is a past president of ASHI, the American Society of Home Inspectors and is a Florida home inspector and home inspection educator. Mr. Cramer serves on the ASHI Home Inspection Standards. Contact Mark Cramer at: 727-595-4211 mark@BestTampaInspector.com
- John Cranor is an ASHI member and a home inspector (The House Whisperer) is located in Glen Allen, VA 23060. He is also a contributor to InspectApedia.com in several technical areas such as plumbing and appliances (dryer vents). Contact Mr. Cranor at 804-747-7747 or by Email: johncranor@verizon.net
 Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. (416) 964-9415 1-800-268-7070 info@carsondunlop.com. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides:
- Commercial Building Inspection Courses - protocol ASTM Standard E 2018-08 for Property Condition Assessments
- Home Inspection Education Courses including home study & live classes at eleven colleges & universities.
- Home Inspection Education Home Study Courses - ASHI@Home Training 10-course program.
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on these courses: Enter INSPECTAHITP in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
- The Home Reference Book, a reference & inspection report product for building owners & inspectors.
Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
- The Home Reference eBook, an electronic version for PCs, the iPad, iPhone, & Android smart phones.
Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter inspectaehrb in the order payment page "Promo/Redemption" space.
- The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors.
Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page "Promo/Redemption" space.
- The Horizon Software System manages business operations,scheduling, & inspection report writing using Carson Dunlop's knowledge base & color images. The Horizon system runs on always-available cloud-based software for office computers, laptops, tablets, iPad, Android, & other smartphones.
- Leaky Heating Oil Tanks - Advice for Home Owners or Buyers: caused of leaks in oil tanks, oil tank testing alternatives, what to do about leaky tanks: D. J. Friedman, ASHI Tech. Journal, Vol.2 No.1, Winter, 1992 p. 42-43 Illus
- Leak or Failure Rates for Home Heating Oil Tanks
- Legal Issues Regarding Buried Oil Storage Tanks K. S. Rea, Attorney, summary from ASHI Chapter Seminar.
- Primer on Petroleum Bulk Storage Tanks & Petroleum Contamination of Property Paul H. Ciminello, ASHI Tech. Journal, Vol.3 No.1 Spring 1993, p 35-39
- Petroleum Bulk Storage J. Sibblies, NY State DEC, Advice to Home Owners and Home Inspectors about Oil Storage Tanks - summary from ASHI Chapter Seminar.
- "How do you choose the right tank testing method?", Cynthia Johnson, Fuel Oil & Oil Heat Magazine, November 1995
- National Association of Oil Heat Service Managers, PO Box 380, Elmwood Park, NJ 07407
- "Homeowners Guide to Fuel Storage," Agway Energy Products, Verbank, NY, November 1990
- ...
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
 The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
Or choose the The Home Reference eBook for PCs, Macs, Kindle, iPad, iPhone, or Android Smart Phones. Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter INSPECTAEHRB in the order payment page "Promo/Redemption" space.
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