Photograph of  Half-Buried Indoor Oil Storage Tank Used Outside below a ready to collapse deck Guide to Heating Oil Fill, Vent, & Oil Burner Feed Piping Defects & Leaks

  • OIL TANK PIPING & PIPING DEFECTS - home - CONTENTS: piping errors leading to oil leaks in heating oil piping, fittings, oil filters, oil burners, in turn lead to expensive cleanups or loss of heat. Table of normal vacuum readings on heating oil piping systems.
  • POST a QUESTION or READ FAQs about leaks or installation problems in heating oil piping for oil-fired heating equipment & water heaters
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Causes & locations of heating oil leaks in heating oil piping, fittings, oil filters, oil burners: this oil burner fuel piping article describes defects in heating oil piping, filters, safety valves, and oil tank fill and vent piping. All of these oil storage tank and piping installation defects can easily be found by visual inspection.

We include considerations of oil pipe leaks out (fuel oil leaks), oil piping leaks in (air in the system), clogged, damaged, noisy, or mis-routed fuel oil piping, and oil fill and vent piping size and location requirements.

We also discuss the need for and location for heating oil or fuel oil filters and safety valves. Beyond the costly problem of leaky oil piping, this document lists other important safety or oil-fired equipment operational defects in home and light commercial heating oil storage and piping systems.

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Heating Oil Fill, Vent, & Piping Leaks & Defects: How to Find, Fix, or Report Oil Piping Defects by Visual Inspection

Heating oil delivery by Bottinin Fuel (C) Daniel FriedmanWhy is this heating oil delivery operator leaning with his ear next to the vent pipe on this building during a fuel delivery? And why is he standing on a ladder? These are examples of topics we explain in this article and are discussed further at OIL FILL / VENT PIPE LEAKS.

[Click to enlarge any image]

In addition to explaining and illustrating common defects in heating oil piping at the oil tank and between the oil tank and the oil burner, we also include sample home inspection report language that may assist home owners or home buyers in understanding risks associated with both buried and above ground oil or other fuel storage tanks at their property.

A Maryland study found that more than 80% of petroleum product storage tank leaks occurred in the piping system, not the tank itself, and that leaks were not correlated with age of the storage tank and piping.[3]

Article Series Contents

Proper oil tank and oil piping inspection report language explains the need for action and indicates where more information can be obtained. Also see text and oil tank defect photographs at Visual Inspection of Oil Storage Tanks.

NOTICE: while example report language is provided here, reproduction of this or any of our web pages or their contents online at other websites or in printed documents for sale is prohibited. Readers are welcome to use the text directly in home inspection reports, with citation of the InspectAPedia website source.

Undersized Heating Oil Fill or Vent Pipes risk oil tank leaks or damage

Undersized oil piping schematic (C) Carson Dunlop Associates

As Carson Dunlop Associates' sketch shows, oil filler or vent piping that is too small can result in too much pressure in the oil tank during filling, resulting in a burst oil tank and serious oil leakage.

Oil tanks are usually filled under pressure (not by gravity like your car). We also do not like to see plastic oil piping used for these applications, out of concern that it may be broken, leading to a serious oil spill.

More about oil tank fill & vent pipes is at OIL FILL & VENT PIPING.

And see OIL TANK PRESSURE for a detailed explanation of the pressures that occur during normal oil storage tank filling procedures.

Heating oil storage tank fill & vent pipes too far apart risks over pressurized tank, oil leaks

Typical oil tank fill and vent piping details (C) Carson Dunlop Associates

Carson Dunlop's sketch at left shows typical oil fill and vent piping details for an oil tank installed inside of a building. Usually these pipes are located together and against the building wall.

Sometimes we see that the oil filler pipe for an outdoor buried oil tank will be directly over the tank (and perhaps too close to ground level to keep water out), while the installer may have placed the vent pipe some distance away, against the building wall.

This may have seemed to be a neat job for the installer, but you should know that the oil delivery driver listens to the oil vent pipe to hear when the oil tank has been filled.

Placing the vent line too far from the oil tank fill line is risky.

Heating Oil Fill & Vent Pipes Located Too High on the Wall Make Delivery Difficult & Risk Leaks & Spills

Typical oil tank fill and vent piping details (C) Carson Dunlop Associates

The fill & vent piping for an oil tank should be located at a convenient height above ground that is neither too low (our previous example above) nor too high to permit the oil delivery operator to reach the fill pipe and listen at the vent pipe.

In our photo the driver from Bottini Fuel (Poughkeepsie NY) is standing on a ladder we left next to a large rock, both placed to permit the operator to both reach the fill pipe and listen closely at the vent pipe to determine when the oil tank (not in view) is filled.

Making it easy for the driver to listen to the fill alarm or vent pipe reduces the chances of seepage, over-filling, or leaks at the oil tank.

At the property shown, renovations lowered the ground level by about 24", making this fill & vent pipe a bit height. This driver told us he has been delivering oil to this property for a decade, so he's quite good natured about stepping up to the piping using the rock or ladder.

But a heating oil delivery person does not carry a ladder on the oil truck, nor is s/he obligated to dig around in the property owner's stuff to find something to stand on. Making the driver perform extra tasks adds time and trouble to a job whose performance is often measured by the oil company in the number of deliveries accomplished in the day.

Improper oil fill or vent piping, missing cap, wrong fittings risk water leaks into outdoor or buried oil tanks

Heating Oil Tank Fill or Vent Pipe Caps Lost or Clogged

Oil tank fill and vent caps (C) Carson Dunlop Associates

As Carson Dunlop's sketch shows above, and as we show in Arlene Puentes' photo below, you are asking for water in the heating oil tank or insects clogging the fill or vent line (probably the vent line) if the caps have been lost from these pipes.

Missing oil filler caps (C) Daniel Friedman

We've been informed of oil tank fill difficulties (perhaps even leading to a burst or oil tank leak) when insects clogged the oil tank vent pipe.

If the screen is lost from your oil tank vent pipe be sure to replace it to keep the wasps and mud-daubers out of this line. And be sure the screen on the oil tank vent pipe has not been blocked by painting over it - as we explain
at OIL TANK PRESSURE for an explanation. this can cause an oil tank leak during an oil delivery.

No Heating Oil Tank Vent Pipe or Blocked Oil Tank Vent Pipe

Be sure that you can find a proper oil tank vent pipe. On occasion we find that a filler pipe was installed but no vent pipe was run outside. Improper oil tank venting such as no tank vent at all, a too-small oil tank vent, or a vent which is improperly installed, routed, or has become blocked, can cause a catastrophic oil spill in a building or outdoors at a buried tank.

Oil fumes and even heating oil may spill into the building. The tank should be vented to outside to avoid dumping noxious and possibly combustible or obnoxious fumes into the living area.

Outside Exposed Oil Storage Tank Fill or Vent Pipe Admit Water

Check to see if the oil tank fill pipe is in a location where roof drainage may fall directly on or into it. Water in an oil tank can lead to loss of heat and costly related damage from that condition or it can accelerate rust and corrosion from inside the oil tank, leading to oil leaks and a costly environmental cleanup. The tank should be tested for the amount of water in it and if in question, it should be tested for leaks. And protect the fill pipe and vent from water entry.


Oil Tank Fill or Vent Pipe Not Sealed at Wall - Oil Tank - Caulk pipe entrances

You should caulk the opening where tank supply and vent pipes penetrate the house wall, to prevent pest or water entry at this point. This is an inexpensive item. This repair/maintenance item may be deferred.


Oil Supply Line Piping Defects between oil tank and oil burner

Causes of Leaks in Heating Oil Piping Between the Oil Tank & the Oil Burner

Details listing the various sources of oil piping leaks between the tank and the burner are now at OIL LINE PIPING LEAK CAUSES.

SINGLE HIGH OIL LINE - Oil Line Problem: single line routed high may lose prime

SERVICE NOTE: if an oil burner's fuel unit is served by a single line from a buried oil tank, or if the oil line is routed from even an indoor heating oil tank up high beneath the ceiling and back down to the oil burner, in some circumstances this installation may tend to lose prime in oil piping system, become air locked, or these events can lead to loss of heat and possible damage to the building from frozen pipes.

This problem occurs commonly if the oil tank is remote and buried (oil burner pumps don't have much lift capacity), or when an indoor tank is very low on oil. You should review this installation detail with your service person.

See our discussion of check valves and the Tigerloop™ product and also
see OIL TANK PRESSURE for alternatives to conversion of a single line to a two line oil supply piping system.

Single Heating Oil Line on a Buried Oil Storage Tank - Single oil line on buried oil tank risks lost prime, no heat

A single oil line was found coming from tank to oil burner. Recommended practice is use of two pipes, for several reasons: avoiding loss of prime, providing alternate pipe if supply pipe clogs, and reducing the lift load on the pump.

Note: some experts recommend that the fire-safety valve for these systems be installed ONLY on the supply line, with only a simple check valve on the return line. This procedure reduces the risk of burst gasket at the oil pump and spray of heating oil into an existing fire should a valve on the return line close before the valve on the supply line during a fire.

Heating Oil Line Leaks: oil out & air in risks loss of heat & risks a puffback

Heating oil pipeline leaks (C) Daniel FriedmanWatch out: leaks in heating oil appliance piping or filters can be much more serious than just a drip spot on the floor. Oil leaks may be hazardous and can lead to improper system operation and even loss of heat in the building.

We discuss the causes & effects of heating oil piping leaks in detail at


Reader Question: How frequently do the copper oil lines leak from corrosion or other factors?

Contractor renovating my basement enclosed the fuel oil line (tank to burner) in the walls. Just after having carpet laid, I was reinstalling baseboards and my nail gun made a perfect nail hole in the hidden piping. About 2 qts. oil all sprayed out. I shut off tank valve and ran furnace to use up oil in lines. It will be a massive clean-up and I don't want to have this happen again.

How frequently do the copper lines leak from corrosion or other factors? What are the options to prevent a future leak? - Judy 4/23/12

Reply: Frequency of Heating Oil Piping Leaks by Leak Location, Type, Source, Cause

Judy, statistics on oil tank leaks are discussed at OIL TANK LEAKS & SMELLS. While those data focus on and report leaks as oil tank leaks, actually some of the leaks reported under the aegis of "oil tanks" may actually occur in the oil supply and return piping (on a two pipe system for buried tanks) or on the oil supply line from an above-ground oil tank.

But I have not found studies, reports, nor statistics on the leak occurrence rate in just heating oil piping itself. In my experience, small leaks in the oil piping system are not uncommon. But as leaks in the supply line lead to faulty oil burner operation, ultimately they lead to a diagnosis and repair. (See the previous Q&A about vacuum tests and pressure tests on oil heat piping and on fuel units respectively.)

Oil Piping Leak Report of 0.005 in New England

At OIL TANK FAILURE RATES we include a section on reports of frequency of heating oil piping leaks. You will see that studies found the leakage rate in New England in the U.S. at about five leaks per thousand customers or less, depending on the sub-area in the study.

Oil Tank Leak Report of 40% with 82% due to Oil Piping in Maryland

In a 1986 study Diane H. Heck found leaks in 40% of petroleum fuel tanks (diesel fuel or kerosene K-1, heating oil, waste oil, and gasoline tanks), (n=240). More accurately she reported a 40% leak occurrence rate in oil storage tank installations, because 82% of those leaks were traced to leaks in oil piping![3]

Because gasoline tanks were included in this study, several factors may lead readers to think that a higher proportion of leaks occurred in gasoline storage tanks than in heating oil or kerosene storage tanks. But as we report
at OIL TANK FAILURE CAUSES that was not the case. Gasoline tanks were responsible for only 26% of all of the leaks found.

Opinion about Probable Percentage of Types of Oil Piping Leaks

My opinion based on field experience repairing heating systems and on field experience as a building inspector of several thousand buildings is that among the leaks that do occur in oil piping systems, they occur in roughly this frequency by type:

This is because most often the heating oil piping is exposed along a garage or utility area floor or ceiling and is not buried in walls. Certainly if an oil line were to be installed running hidden inside a wall or floor I'd be nervous about including any fittings whatsoever, as it is at the fittings that the leak risk is greater.

In the OIL TANK PIPING & PIPING DEFECTS article above, in a section titled Defects Found in Heating Oil Piping Between the Oil Tank & the Oil Burner, we catalog the types of leaks that occur in oil piping and where they are found. We also describe steps that can be taken t protect oil piping lines from future damage, including a nail puncture such as your oil piping line suffered.

In the Technical Reviewers & References section below we include additional citations on oil piping leak detection & frequency.

Heating Oil Supply Pipe Leaks in the Heating Oil Line at the Oil Filter

Heating oil pipeline leaks (C) Daniel Friedman

At OIL FILTERS on HEATING EQUIPMENT we described changing the oil filter as part of oil burner maintenance.

And there we also warn about leaks in piping fittings at the burner and we give a detailed description of exactly why and how leaks occur at the heating oil filter. at the oil filter canister assembly. An except is below.

Oil piping leak at the copper piping flare fitting

As we explain earlier in this article, and as we elaborate
at OIL BURNER INSPECTION & REPAIR, oil leaks in the oil piping and filter system can not only spill oil, but can lead to loss of heat, improper oil burner operation and even a puffback.

At left we illustrate an active oil leak at a flare fitting.

We don't know without further investigation if this leak is because the flare nut is loose or if it's because the copper flare was cracked or improperly made, or finally, if it's because of a notch or scratch on the brass mating surface of the flare.

Try gently tightening the fitting and then clean it thoroughly and check for leaks.

Heating Oil System Filter Omitted - No Oil Filter Installed on Oil Fired Equipment

Heating oil filter at the oil burner (C) Daniel Friedman

Details about heating equipment oil filters are found
at OIL FILTERS on HEATING EQUIPMENT. Excerpts are below.

If we do not find a heating oil filter installed on the system this is a defect that risks loss of heat.

Most modern oil heating equipment will have an oil filter installed, such as the one shown in our photo at left.

Notice that there's a heating oil leak below the connection to the filter outlet? This leak will suck air into the oil burner when it's running, leading to improper and possibly unsafe operation, risking a puffback.

Unless you find or the owner can point out a filter already in place, we recommend installation of one - to be located at or very near the burner and "downstream" of a fire-o-matic safety shutoff valve to permit easy service. Failure to provide adequate filtering may lead to loss of heat and subsequent damage to the building.

DUAL HEATING FUEL OIL LINE - improper installation of oil line shutoff valves

On oil fired heating equipment systems that use an open loop oil piping system or dual oil line piping arrangement (such as used with buried oil tanks and at other installations where the oil burner fuel unit may otherwise lack adequate lift and pumping capacity), the fusible-link type heating oil line shutoff/safety valve should be located only on the oil supply line at the oil burner.

Dual oil line hookup at oil burner (C) D Friedman

At above left we illustrate a typical dual oil line piping arrangement exiting at the top of an oil storage tank. Notice incidentally that under-sized takn vent line in the upper right ofthe phtoto.

Dual oil line hookup at oil burner (C) D Friedman

Our dual line oil piping hookup photo above llustrates at least one thing right: there is a fusible link shutoff valve only on the incoming oil line and not on the return line.

We'd like to see a check valve on the return line, and a cleaner site. Heating service techs are accustomed to having to work in cramped dirty locations, but the tighter and nastier the space, the more difficult the job becomes, and the less time anyone wants to spend doing it.

Often the result is "deferred maintenance" - the heating equipment is simply not properly maintained at all.

Do not install a second fusible-link fire safety valve (OSV) shutoff-valve on the return oil line. Use a check valve instead. Details are

OIL LINE SHUTOFF VALVE - missing or improper location

The proper location for the oil line shutoff valve with a fusible link (Fire-o-Matic™ type valves) is just before the oil filter and close to each individual oil burner. Details about oil line valve installation and operation are

Reader Question: how to get a water & debris-clogged heating oil line flowing after hurricane & flood damage

I am having problems restarting the water heater ever since hurricane irene slammed into New Jersey and my basement flooded. We changed the motor and oil filter, but are having problems getting oil to feed through the lines I was wondering if there were suggestions. - Antoinette

Reply: Guide to How to clear or un-block a clogged heating oil line by CO2 blasting, filter changeout, or oil line replacement


When an oil fired water heater has been flooded, such as by hurricane Irene, there are a number of concerns that need to be addressed. You have taken two obvious steps by changing parts (motor and oil filter) but I can add a few suggestions that might help.

Details about unclogging oil lines are found

Oil lines can become blocked with sludge, silt, mud, even water if the lines are open to the flooding environment. Normally an oil line between the oil tank and oil burner, say at a water heater, is always full of fuel oil, and sealed against oil leaks out and air leaks in to the piping system. So dirt or water from outside the system would not easily enter the piping system.

But if the oil tank itself were flooded you might have water and mud or silt and dirt on the tank bottom - if your oil line feeds from the tank bottom all of that crud would enter the oil line. So a further check of the condition of the oil tank is in order.

A buried oil tank should, like the oil piping, be sealed against outside water entry (though in times of area flooding a partially empty oil tank might float-up and break lines or cause leaks).

An above ground oil tank should be ok IF flood waters never rose high enough to enter the oil tank vent or fill piping.

If your oil tank itself checks out as not contaminated with water and dirt, and provided we are sure that the oil burner assembly was itself entirely replaced and that the oil pump (fuel unit) is working properly, and if you are unable to draw oil from the tank, the usual step employed by the service tech is to use a CO2 gas cartridge and special "gun" assembly that connects to the oil line and attempts to "blow out" an obstruction.

If you are unable to make the line usable following that procedure, and provided we remain convinced that the line is the culprit, I'd have the service company run a new fuel line between the oil tank and the burner.

I'd also be sure the service tech was following proper procedure for bleeding air out of the oil piping during service restoration.


VacuumTesting Oil Lines Detects Both Blockage & Leaks: Vacuum Standards for Oil Supply Piping

This topic has been relocated to OIL LINE VACUUM & PRESSURE TESTS - How pressure & vacuum gauges are used on heating oil lines to check for leaks or fuel unit troubles.

At OIL PUMP FUEL UNIT we include at Frequently Asked Questions (about fuel units) section that provides a detailed explanation of how to read a pressure gauge on the oil piping system (at the fuel unit) to diagnose a leak or similar problem at the fuel unit.

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