Oil tank gauge types, and which one fits your tank

The five things sold as an oil tank gauge

Most above-ground steel tanks in the Northeast have the first one. A float rides on the oil at the end of a hinged arm, and as the level drops the arm moves a disc in the clear vial you read from the top of the tank. There are no electronics, no battery and nothing to calibrate, which is why these outlive the tanks they sit on. What the marks mean, and the four ways the gauge lies, are in reading an oil tank gauge.

The whistle in your vent line is a vent alarm, not a level gauge. It reads no level at any point: it whistles while displaced air leaves the tank during a fill, then goes quiet when rising oil reaches the bottom of its tube, and that silence is what tells the driver to stop. The tube length is what sets the air gap, so a delivery always stops short of the shell's computed capacity. An upright 275 computes out at 274 gallons full. A normal fill into an empty one runs 230 to 250 gallons, and about 240 of that is oil the burner can reach, because the last few gallons sit below the outlet pickup. That is three different numbers on one tank. A Roth 1000L falls short of its name for a separate reason: its F mark and its 263 gallon ceiling are the 95 percent fill limit on a tank sold as a 275.

Which gauge fits which tank

Three questions settle this. Is the tank above ground or buried. Is it a steel oval or a sealed Roth. Is it one tank, or a pair piped together. Answer those three and you know which part to order.

The Amazon links above are affiliate links: as an Amazon Associate this site earns from qualifying purchases, at no extra cost to you, and it does not change which gauge is right for your tank. Roth gauges are ordered by part number through a Roth dealer or a supply house rather than from Amazon.

The second number on a steel tank is the thread. These gauges are sold in 1.5 inch and 2 inch male NPT, and the tapping on your tank decides which you need. Pull the old gauge or read what is written on it before ordering rather than guessing from a photo. Sizing, the thread, and the trap that turns a small job into vent piping work are all in replacing an oil tank gauge.

If what you want is the level on your phone

That is the ultrasonic category, and it is a different purchase with its own requirements. The sensor pulses sound down from the top of the tank, times the echo off the oil surface to get the air gap, then subtracts that gap from the tank height you configured during setup. Configure the wrong tank and every reading is wrong, so know which tank you have before you order. How that plays out day to day is in WiFi and smart oil tank gauges.

• A genuinely spare 2 inch tapping. The Smart Oil Gauge fits a 2 inch NPT tapping, roughly 2.375 inches across the threads, with a 1.5 inch adapter available. A spare tapping is one with nothing in it but a plug, and most of a tank's tappings are already spoken for by the fill, the vent, the gauge and the supply line.
• About 6.2 inches of clearance above the tank, to reach the batteries later. Low basement joists are the usual problem.
• 2.4 GHz WiFi that reaches the tank, not 5 GHz. Check the signal where the tank sits, not where the router is.
• Two lithium AA cells, rated 1 to 2 years, with a 24 hour upload interval recommended. Checking hourly costs battery and tells you nothing new.
• On an outdoor tank, seal the white cap with Teflon tape or equivalent. The manufacturer requires it, and skipping it voids the warranty.
• Check your tank is on the list. The published compatibility covers standard vertical or horizontal 138, 220, 240, 275 and 330 gallon tanks, plus 500 and 550 gallon above-ground cylindrical tanks. Roth tanks need an adapter, and the manufacturer lists the 400L, 620L, 1000L and 1000LH but not the 1500L.

Those requirements are the Smart Oil Gauge's own, since it is the connected unit this section is describing: the Smart Oil Gauge listing on Amazon. (Affiliate link: this site may earn a commission at no extra cost to you.) If you would rather not involve WiFi at all, the same ultrasonic sensing is sold with a local display: Beckett's Rocket sends 915 MHz radio to a plug-in indoor receiver up to 150 feet away, with no app, an LCD bar display, a low-fuel icon under 20 percent and an alarm under 10 percent, and a transmitter cell rated past 10 years. It is sold through heating-oil dealers and installed by a technician, so ask your oil company about that one.

Ultrasonic specifications are quoted from each manufacturer's published product pages, not from hands-on testing. Features and compatibility change, so confirm against the current spec sheet before buying.

Reading the gauge you have

Every one of these reads a different quantity, and the common mistake is treating the number as gallons when it is not.

• Float gauge. The marks are depth fractions, not gallon fractions. On a 275 vertical, gauge 1/2 is about 137 gallons and gauge 1/4 is about 58, against 69 for a true quarter of the tank's 274 gallon computed capacity. The bottom of the tank curves away, so the lean part of the tank is exactly where you are deciding whether to order. The full table is in reading an oil tank gauge.
• Roth gauge. Coarse fractions, and its F mark sits at the 95 percent maximum fill level rather than at geometric full. Sizes and models are on the Roth tank page.
• Remote pneumatic gauge. Pump a few steady strokes and read inches at the top of the red column, then convert on the chart for your tank. After service work on the line it can take around 25 strokes to purge the system. A healthy gauge holds the reading instead of bleeding back down.
• Ultrasonic monitor. Expect the word Full rather than a number for the first few inches after a delivery, because the oil sits too close to the sensor for a clean echo. While your WiFi is down it reports nothing, and it picks up again when the connection comes back.

Whichever of the five you have, the gauge is a trend indicator, good at "lower than last week". A stick reading converted on the tank's own chart is the number worth placing an order on, and the two minute procedure is in how to stick an oil tank. The metered delivery ticket is the truth for a brim-full tank. If your tank cannot be read at all, because the vial is fogged, the tank is sealed or the buried fill pipe defeats a stick, tracking oil without a gauge covers the four ways to keep heat in the house without one.

Replacing one, and the two swaps that are not yours

A plain float gauge is a reasonable homeowner job, and it comes with fixed conditions. The float goes in held all the way up: take the vial off, hold the indicator with one hand and work the wrench with the other. Run the float down the tank's long axis, clear of the fill, because oil landing on a delivery will twist or break a float sitting underneath it. Hand-start the threads, use a pipe dope rated for oil such as Pro Dope or Gasoila, and do not overtighten a plastic body. Then have the delivery driver inspect the tapping before the next fill, because a seeping tapping is easy to miss from a basement doorway and a driver spots it in seconds. Every step, with the reasons, is in replacing an oil tank gauge.

A Roth sealed gauge is the exception to the sealant rule, so read it before you reach for the dope. It seats on one of the plastic adapters supplied with the tank and seals on an O-ring, so it is hand-tightened and takes no pipe dope and no tape at all. Let the string and float down slowly as it goes in, or you can damage the gearing or unspool the line off the reel.

Sight glass and sight gauge are not the same thing

When a homeowner says sight glass, they almost always mean the clear plastic vial on top of their float gauge, where the disc moves. Oil never enters that vial. It is part of the gauge, it is sold on its own when it fogs or cracks, and on an outdoor tank it is the usual casualty.

A true sight gauge is a different device: a clear tube run vertically outside the tank and plumbed into it at the bottom outlet, so the tube fills with oil to the same level the tank holds. Continuous models isolate the tube with a valve at rest; push-button models stay isolated until you press the button. The vendors who sell them describe them as a significant potential leak source, and note that bending the tube over with the button pressed pours oil out. The products that exist are imported domestic parts, not US residential ones.

The same naming habit is why the whistle keeps getting called a gauge. Two separate jobs happen at the tank and each has its own device: the gauge tells you how much oil is in there, the vent alarm tells the driver when to stop pumping, and neither one does the other's work. That second job is not optional. NORA's tank manual requires a vent alarm on every above-ground tank, and its recommendation to the industry is three words, "No Whistle, No Fill."

The sight gauge description here is taken from the published listings and installation notes of the UK and Ireland vendors who sell them, not from hands-on testing, and no US residential part of this kind is quoted. For what is permitted on your own tank, ask your oil company or your local inspector. The NORA points are restated from the vent alarm guide.

Related

• Reading a float gauge, and the four ways it lies
• Replacing an oil tank gauge
• WiFi and smart oil tank gauges
• How to stick an oil tank