Tanks should be listed and labeled, and conform to standards for underground and above-ground tanks. The maximum amount of fuel oil stored above ground or inside a dwelling should be 660 gallons (2,498 L). The cross-connection of two tanks is permitted if the total aggregate capacity does not exceed 660 gallons. Gravity flow from one tank to another is permitted, provided that the two tanks are on the same horizontal plane. 14.1.1 Inside and Outside
Oil storage tanks for use inside of dwellings should be of such size to permit installation and removal from dwellings as whole units. Any oil storage tank larger than 10 gallons (38 L) should be at least 5 feet from any fire or flame of any fuel-burning appliance.
Tanks located outside and above ground should be at least 5 feet from an adjoining property line. Tanks located outdoors should be protected from the weather and from physical damage. Tanks should have a fuel-level gauge, but glass gauges should not be used. In areas prone to flooding, tanks should be installed at or above the flood elevation, or should be anchored to prevent floatation, collapse or lateral movement under flood conditions.
14.1.2 Oil Tank Supply
Exterior above-ground fill and vent piping should be removed when tanks are abandoned or removed. Fill piping should terminate outside of the dwelling at a point at least 2 feet from any building opening at the same or a lower level. Supply piping should not be smaller than 3/8-inch pipe, or 3/8-inch outside-diameter tubing, and the copper tubing should be a minimum of Type L.
14.1.3 Oil Tank Vents
Vent piping should not be smaller than 1-1/4-inch pipe. Vent piping should slope toward the tank. The lower end of the vent pipe should enter through the top of the tank. Vent piping should terminate outside of dwellings at a point not less than 2 feet, measured vertically and horizontally, from any dwelling's opening.
14.1.4 Oil Supply Lines
Oil supply lines move the oil from the storage tank to the burner at the equipment or appliance. They are typically made of 3/8-inch copper tubing. If the copper supply oil line passes through a concrete floor or wall, then provision should be made for lateral thermal expansion and movement of the pipe. In general, the oil supply piping should be installed in a manner that avoids placing stress on the piping and accommodates the expansion and contraction of the piping system and building materials. This may be accomplished with a plastic or rubber sleeve. Buried piping should be protected by corrosion-resistant coatings, special alloys, or fiberglass-reinforced plastic. Refer to your local plumbing code for specific requirements.
An oil filter and a shut-off valve should be installed on the supply line coming from the oil storage tank.
14.1.5 Oil Tank Defects
Common problems include leaks at the oil tank, strong odors, improperly supported legs, rust and corrosion damage at the tank legs, missing caps at the pipes, a damaged gauge, and/or excessive rust and corrosion on the tank. An oil filter may be missing, leaking or dirty. Thank you www.nachi.org