Guide to Heating Oil Piping for Duplex or Paired Oil Storage Tanks InspectAPedia® -
How duplex oil storage tanks are piped for fill, vent, & oil lines
Heating oil tank fill and vent pipe requirements
Where should oil line fire safety valves and check valves be located?
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This document describes the typical piping arrangements for heating oil storage tanks: how the oil tank fill, vent, and supply piping are arranged when two oil storage tanks (or more) are installed at a building.
TYPICAL OIL TANK PIPING for DUAL OIL TANKS INDOORS
Quick Guide to Fill and Vent Piping for Duplex Heating Oil Storage Tanks
At buildings where two heating oil storage tanks are installed, typically indoors, this Audel Oil Burner Guide sketch shows the proper arrangement of fill piping, vent piping, and oil line piping leaving the tanks.
We have seen an alternative arrangement that provides a fill line only to the first tank, with the second tank filled by a second pipe exiting the top of the first oil tank - not an arrangement we recommend as this forces the first oil tank to be fully pressurized at the oil delivery truck pressure during fill-up of the second tank.
The piping shown in this Audel sketch is better.
Thanks to Arlene Puentes for technical editing, March 2010.
Here are more details of dual oil storage tank piping
Our photograph of duplexed or a "pair" of oil storage tanks in a residential basement shows (left) [click to enlarge the photo) shows the most common oil fill, vent, and copper oil supply piping arrangement when two oil tanks are installed side by side at a building.
The oil tank filler pipe is connected to the first oil tank (the rear tank of the pair in our photo) at an oil tank top inlet fitting accepting a 2" diameter filler pipe.
A second tank top tapping is used to continue the same diameter 2" steel piping out of the top of tank 1 and into the top of tank 2.
The oil tank vent pipe is connected from the top of the second oil tank (the tank fully shown or "front most" in the oil tank pair in our photo) and routed outdoors to a location close to the filler pipe (so that the oil tank delivery driver can monitor the fill-up progress in the duplexed oil storage tanks.
The oil tank level gauge is on tank #2 in our photo but would work equally well on either tank.
Copper oil supply piping is connected at the bottom outlets of both oil tanks so that as oil is drawn from this heating oil storage system both tanks supply oil to the heating appliances, and thus the oil level will be the same in both tanks at all times. A tee in the copper oil piping taps off of the common line between the two tanks to feed oil to the heating appliances in the building, where you will typically also see a shutoff valve (aiding in service such as changing the oil filter).
At installations that include a fire safety valve at the oil tank (useful for service in this case) we like to see an additional fire safety valve at each oil burner oil supply line since that's a spot where a fire is more likely to occur. See FIRE SAFETY CONTROLS.
As Carson Dunlop Associates' sketch (left) demonstrates,
the fill and vent piping for oil storage tanks must be of adequate diameter (typically 2" filler and 1.5" to 2" vent though older tanks may use 1 1/4" vents),
properly located (vent not too distant from filler), and
protected against water entry or insect nest blockage of the vent line.
Thanks to reader
D. B. Harlow for asking about how to make the proper connections to have two storage tanks, in parallel.
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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
Audels Oil Burner Guide, Installation, Servicing, Repairing, Frank D. Graham, 1940's edition (obsolete). Updated versions of this guide are available in various editions, 1947, 1950, 1955, 1958, 1959, 1962, 1965, 1967, and at prices from around $3.00 to nearly $70.00 - useful for simple, clear, but not current, explanation of how heating equipment works. The original retail price was $1.00.
Dave Ferris - M&S Environmental Systems, Dutchess County, New York. Mr. Ferris was an
HVAC expert. Personal communication to DJF 1987. Remove the firematic or
fusible oil supply line valve on return oil-line side - in case of fire if this
one closes first the pump continues to run, blows its seal, and sprays oil all
over the fire. Proper installation is to have a fusible link valve only on the
supply side, and to install a check valve on the return line to prevent
back-siphonage from the tank.
"HUD Regulation for Manufactured Homes; Requirement that Heat-Tape not include a GFCI [ copy on file as /plumbing/GFCI_Heat_Tapes_HUD_CPSC_Letter1994.pdf ] - ", Meeting Log, US CPSC, HUD, Dennis McCoskrie, ESEE, 2/14/1994
Thanks to reader D.B. Harlow for discussing parallel or duplex oil tank piping arrangement, October 2010
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.
More Reading and advice about oil storage tank leak testing
ABOVE GROUND OIL TANK INSPECTIONS - "Visual Inspection of Above Ground Residential Heating Oil Storage Tanks - ASTs" provides photos of common and easily seen tank leaks and defects, and
a description of some easy visual checks of the condition of a visible oil tank, things that you can do yourself
OIL TANK FAILURE CAUSES Oil Tank Leaks or Oil Tank Failure Causes - oil tank leaks are caused by corrosion, damage, soil conditions, other factors
TANK FAILURE RATES Oil Tank Failure Rates - Oil Tank Leak Probability as a Function of Tank Age, Location, Condition, Soil Conditions and Other Factors
OIL TANK WATER CONTAMINATION - how to find out if there is problematic water in an oil tank and how to get water out of an oil tank are explained
Oil Tanks - The Oil Storage Tank Information Website: Buried or Above Ground Oil Tank Inspection, Testing, Cleanup, Abandonment of Oil Tanks
Abandon a Buried Oil Tank, How To - Abandoning Commercial Underground Tanks, Russ Brauksieck, ASHI Tech. Journal, Vol.3 No.1 Spring 1993, P. 40-41 [Reprint]
Buried Oil Tanks - Finding How to Find Buried Oil Tanks and "Nearly Hidden" and Leaky Oil Tanks - photos and text.
Buried Fuel tank - Advice - Buried FUEL Tank - GAS or OIL advice for home buyers, home owners, inspection report language for homes where a buried oil tank is or was installed
Petroleum Bulk Storage J. Sibblies, NY State DEC, Advice to Home Owners and Home Inspectors about Oil Storage Tanks - summary from ASHI Chapter Seminar.
Septic Tank inspection, testing, diagnosis, repair
OIL TANK FAILURE CAUSES - Oil Tank Failure Causes - oil tank leaks are caused by corrosion, damage, soil conditions, other factors
Tank Failure Rates - Oil Tank Failure Rates - Oil Tank Leak Probability as a Function of Tank Age, Location, Condition, Soil Conditions and Other Factors
OIL TANK TESTING - - How Oil Tanks are Tested for Evidence Leaks, of Current or Previous Oil Spills
"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
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