How big should a bulk fuel tank be?
Big enough that your usual delivery cycle fits inside the usable volume, with a reserve on top, and no bigger than the rated size you can fill safely. The arithmetic is short.
Say your site burns 1,500 gallons of diesel a week. Every number below is illustrative, so swap in your own.
- Pick a delivery cadence. You want a truck every two weeks. That is 3,000 gallons per delivery.
- Add a reserve. Keep one week of burn (1,500 gallons) in the tank when the truck arrives, so a late truck or a cold snap does not stop the work.
- Add them up. You need 4,500 gallons of usable volume.
- Convert usable to rated. If usable volume is about 85% of rated (90% fill ceiling minus a 5% bottom, see the next section), 4,500 / 0.85 is about 5,300 gallons. Tanks come in standard sizes, so you round up to 6,000.
What is the difference between rated and usable capacity?
Usable capacity is what is left after you subtract the empty space you must leave at the top and the fuel you cannot pump out of the bottom. The rated size on the nameplate is the total volume.
For underground tanks, the federal rule sets the point by which overfill equipment must act. Under 40 CFR 280.20(c)(1)(ii), overfill prevention equipment must do one of three things, including “automatically shut off flow into the tank when the tank is no more than 95 percent full” or “alert the transfer operator when the tank is no more than 90 percent full”. The third option is timing- and fitting-based rather than a percentage: it restricts flow 30 minutes before overfilling, alarms one minute before, or shuts off before the top fittings are exposed, and the section has exceptions. So under the two percentage options, the equipment must shut off flow by 95 percent full, or alert the operator by 90 percent full. Plan deliveries to stop short of that point.
For aboveground tanks, the fill limit can come from the manufacturer, your fire code and your supplier’s rules, so use the number in the tank’s documentation. The unpumpable bottom depends on where the suction pickup sits, so check that with the manufacturer as well.
In this post’s example, the fill ceiling and the unpumpable bottom are separate: usable volume is the fill ceiling minus the bottom. As placeholders, borrow the 90% alert point from the underground rule above as a placeholder ceiling (it is not an aboveground standard) and assume a 5% unpumpable bottom. That leaves 85% usable. Neither figure is a standard.
Will a full delivery fit in the tank?
It fits if the fuel in the tank on arrival plus the delivery stays under your fill ceiling. This is the check that catches an oversized order, and overfill prevention at the delivery tank covers it from the driver’s side.
Back to the 6,000-gallon tank, with the placeholder 90% ceiling (5,400 gallons) and the placeholder 5% unpumpable bottom (300 gallons):
| Gallons | |
|---|---|
| Fill ceiling (90% of 6,000) | 5,400 |
| In the tank when the truck arrives (1,500 reserve plus 300 unpumpable bottom) | 1,800 |
| Room for the delivery | 3,600 |
| Planned delivery | 3,000 |
It fits, with 600 gallons to spare. Leave that margin on purpose: the delivery ticket records what the truck discharged, a gauge reads the volume in the tank, and the two can differ a little, especially when the ticket is on a temperature-corrected basis (see gross vs. net gallons). How to read a fuel delivery ticket walks through the fields.
Also think about the truck, since how many gallons a fuel tanker holds shapes what a drop can be. If your drop is small, your supplier may serve you as part of a split load, with other stops on the same run. Ask what minimum drop they will make, because it limits how small a tank can usefully be.
How does tank size change deliveries per month?
Smaller tanks mean more deliveries, and each extra stop is another truck visit. Using the same 1,500-gallon weekly burn (about 6,500 gallons a month), the same 85% usable share (90% ceiling minus 5% bottom) and the same one-week reserve:
| Rated tank | Usable (85%) | Largest drop with 1-week reserve | Deliveries per month at that drop | Aggregate aboveground total, tank alone |
|---|---|---|---|---|
| 1,000 gal | 850 | None: usable is below the reserve | About 8, with no reserve | Under 1,320 |
| 2,000 gal | 1,700 | 200 | About 32, impractical | Over 1,320 |
| 4,000 gal | 3,400 | 1,900 | About 3.4 | Over 1,320 |
| 6,000 gal | 5,100 | 3,600 | About 1.8 | Over 1,320 |
| 10,000 gal | 8,500 | 7,000 (more than one tanker load of diesel) | About 1 | Over 1,320 |
The last column assumes an aboveground tank. A smaller tank costs less to buy, but you pay for it in truck visits and in how often you run close to empty.
Delivery size can also affect what you pay per gallon, because suppliers may price by drop size. That varies by supplier, so ask for their price breaks at each size before you decide. Our post on how to compare bulk fuel quotes covers how to line those quotes up.
When do federal tank rules apply?
Two federal rule sets are worth checking before you buy, because both can change the cost of the project.
Aboveground storage, SPCC. The Spill Prevention, Control, and Countermeasure rule in 40 CFR part 112 exempts a facility that meets both of two tests in 112.1(d)(2): “The completely buried storage capacity of the facility is 42,000 U.S. gallons or less of oil,” and the “aggregate aboveground storage capacity of the facility is 1,320 U.S. gallons or less of oil.” Both counts have listed exclusions, so read the full text. For the aboveground test, “only containers with a capacity of 55 U.S. gallons or greater are counted.” So the 1,320 gallons is a total across the site, not per tank. A 1,000-gallon diesel tank plus six 55-gallon drums of lube or hydraulic oil comes to 1,330 gallons, which is over it. So does that tank plus a 400-gallon generator tank. Above 1,320 gallons, whether the rule covers you depends on the full text of the regulation, so read it or ask your environmental consultant.
Underground storage, 40 CFR part 280. Underground tanks fall under a separate rule set. The requirements in part 280 apply to owners and operators of underground storage tank systems, with some exclusions, and include overfill prevention requirements like the ones above. Your state may run its own program, so check with your state agency.
Your insurer and local fire marshal may have their own limits as well, and neither of those is covered here.
How Energy Connect handles it
This post is general guidance on sizing. It does not describe any Energy Connect feature.
For the DEF side of a site, see bulk DEF delivery on when jugs, totes or a bulk tank make sense. To weigh bulk tank delivery against fueling equipment on site, read on-site fueling vs bulk tank delivery.