Ordering heating oil means balancing two worries: running out in the middle of winter and paying for a delivery you did not need yet. This calculator reads your tank gauge and tells you how much to order, what it will cost and how long it will last.
Reading the tank
Most indoor oil tanks have a float gauge marked in fractions: F, 3/4, 1/2, 1/4. Enter it as a percentage. A 275-gallon tank, the most common size in US homes, actually holds about 250 to 260 gallons in practice; check your tank’s chart for exact figures.
A 275 gal tank at 30% holds about 82.5 gal.
How much to order
Never fill a tank to 100%: oil expands when it warms up, and the delivery driver needs room to avoid overfilling through the vent. Fill to about 90%.
order = capacity × 90% − current oil
In the example: 247.5 − 82.5 = 165 gal, or about $627 at $3.80 a gallon.
Suppliers often have a minimum delivery, commonly 100 to 150 gallons, and charge extra for small orders.
How long it lasts
The calculator spreads your seasonal use over the heating season. Using 800 gallons over 240 days is about 3.3 gallons a day on average, so 82.5 gallons last about 24 days. Cold snaps use much more than the average, so order when the gauge reaches about 1/4, earlier in mid-winter or before a holiday.
For a better estimate, divide your yearly use by the heating degree days of your area to get gallons per degree day, the K-factor many dealers use for automatic delivery.
Cost per unit of heat
One gallon of heating oil contains about 138,500 BTU, or 40.6 kWh. Dividing the price by 40.6 gives the cost per kWh of fuel, before boiler efficiency. With a furnace at 85% efficiency, divide again by 0.85 to compare with electricity or a heat pump.
Saving money
- Buy in late summer when prices are often lower, or ask about pre-buy and budget plans.
- Have the furnace or boiler cleaned and tuned every year.
- Seal air leaks, add insulation and use a programmable thermostat.
- Watch for tank corrosion and leaks; an old steel tank may need replacing.