Heating oil filter at the oil burner (C) Daniel Friedman Guide to Heating Oil Piping for Duplex or Paired Oil Storage Tanks

  • DUAL OIL TANKS - PIPING - CONTENTS: 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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Oil tank piping: how to hook up fill & vent & oil line piping on duplex or dual oil storage tanks: 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.

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Quick Guide to Fill and Vent Piping for Duplex Heating Oil Storage Tanks

Oil tank piping for two tanks (C) Daniel Friedman - Audel

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. [Click to enlarge any image]

Thanks to Arlene Puentes for technical editing, March 2010.

[Click to enlarge any image]

Heating oil filter at the oil burner (C) Daniel FriedmanHere 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.

  1. 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.
  2. 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.
  3. 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.
  4. The oil tank level gauge is on tank #2 in our photo but would work equally well on either tank.
  5. 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).

Oil tank fill and vent pipe details (C) Carson Dunlop AssociatesAt 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.


As Carson Dunlop Associates' sketch (left) demonstrates,

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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