How many gallons of heating oil per day?
It changes with the weather. Suppliers quote about 2 gallons a day in mild weather, around 5 in a Northeast winter and 8 or more in a cold snap, and each is about right for some house. The tables below show how one house moves between those numbers, so you can find where yours sits.
The math
degree days for a day = 65 − average outdoor temperature (°F)
gallons per degree day = gallons burned ÷ degree days over the same weeks
gallons per day = gallons per degree day × degree days that day
EIA uses 65 °F as the base and gives an example: a day with a high of 33 and a low of 25 averages 29, which is 36 degree days (65 − 29). EIA describes degree days as a measure of how much heating a building needs (EIA, degree days). A colder day has more of them, so the house burns more.
Gallons per day by outdoor temperature
Three houses, each burning the season total shown over 5,000 degree days. The 5,000 is my assumption for a cold-winter area, and the season totals are examples. For scale, EIA's winter outlook for 2021-22 expected an average household that heats with oil to use 511 gallons (EIA), between the first two rows.
| Gallons a season | Per degree day | 50 °F | 40 °F | 30 °F | 20 °F | 10 °F |
|---|---|---|---|---|---|---|
| 500 | 0.10 | 1.5 | 2.5 | 3.5 | 4.5 | 5.5 |
| 800 | 0.16 | 2.4 | 4.0 | 5.6 | 7.2 | 8.8 |
| 1,100 | 0.22 | 3.3 | 5.5 | 7.7 | 9.9 | 12.1 |
How long 100 gallons lasts
The same three houses, if every day in a row were at that temperature. Whole days, rounded down.
| Gallons a season | 50 °F | 40 °F | 30 °F | 20 °F | 10 °F |
|---|---|---|---|---|---|
| 500 | 66 days | 40 days | 28 days | 22 days | 18 days |
| 800 | 41 days | 25 days | 17 days | 13 days | 11 days |
| 1,100 | 30 days | 18 days | 12 days | 10 days | 8 days |
A real week mixes mild and cold days, so the answer for your house lands between the columns. For a rough figure, use the column closest to the average temperature you expect.
How long a 275 gallon tank lasts
A delivery rarely fills a 275 gallon tank to the label. The tank chart gives 220 to 248 gallons as the usual maximum fill, so the table starts from both ends of that range. The rows are three example houses by how much heat they lose, as gallons per degree day. The values are my picks for illustration: over the 5,000 degree day season above they come to about 600, 900 and 1,300 gallons. The columns are the average outdoor temperature, held for the whole stretch. Each cell shows the gallons burned per day, then the days a full tank lasts, rounded down.
| Gallons per degree day | 45 °F | 35 °F | 25 °F | 15 °F | 5 °F |
|---|---|---|---|---|---|
| 0.12 | 2.4 gal/day 91–103 days | 3.6 gal/day 61–68 days | 4.8 gal/day 45–51 days | 6.0 gal/day 36–41 days | 7.2 gal/day 30–34 days |
| 0.18 | 3.6 gal/day 61–68 days | 5.4 gal/day 40–45 days | 7.2 gal/day 30–34 days | 9.0 gal/day 24–27 days | 10.8 gal/day 20–22 days |
| 0.26 | 5.2 gal/day 42–47 days | 7.8 gal/day 28–31 days | 10.4 gal/day 21–23 days | 13.0 gal/day 16–19 days | 15.6 gal/day 14–15 days |
Worked example: a house at 0.18 gallons per degree day in a stretch averaging 35 °F. That is 30 degree days a day (65 − 35), so 0.18 × 30 = 5.4 gallons a day. A tank filled to 220 gallons lasts 40 days (220 ÷ 5.4), and one filled to 248 gallons lasts 45 days.
These are days to empty. The burner can start to sputter before the tank is dry, so schedule the next delivery when about a tenth is left. To get your own answer from two tank readings instead of a guess, open the run-out calculator with a 275 gallon tank and a 10% reserve already set.
Find your own number
- Take two dated tank readings a week or more apart and turn them into gallons with the calculator. The difference, plus any delivery in between, is the gallons burned.
- Add up the degree days for those dates from your local weather data. A day's degree days are 65 minus its average temperature, and never below zero.
- Divide gallons by degree days. That is your gallons per degree day, the second column above.
- Multiply by the degree days you expect, or use the run-out page for the days-left math.
What the tables leave out
- Hot water from the same boiler burns oil all year, even on days above 65 °F. The tables treat all oil as heating, so a house with oil hot water burns a bit more than shown on mild days.
- Wind, sun, how often the house is occupied and the thermostat setting move the number from day to day.
- Burner size, boiler efficiency and insulation set the gallons per degree day. Two houses on the same street can differ a lot.
Related
- How long will heating oil last? Days left from your own readings.
- 275 gallon oil tank chart: inches on the stick to gallons.
- Heating fuel cost comparison: what a season of heat costs in other fuels.