Heating degree days (HDD) measure how cold a period was. Fuel use scales with degree days, so last season’s usage per degree day predicts this season’s — for budgets and tank-fill timing.
The example
0.42 gal/HDD, 4,500 HDD forecast.
| A | B | |
|---|---|---|
| 1 | Item | Value |
| 2 | 0.42 × 4500 | — |
| 3 | Fuel | → ~1,890 gal |
The formula
The formula:
How it works
How it works:
- Fuel per HDD = last season’s fuel ÷ that season’s degree days — your home’s heating rate.
- Multiply by the forecast HDD for projected usage.
- Use it for budget (gallons × price) and refill timing.
- A degree day = each degree the daily mean is below 65°F, summed over days.
Degree days turn weather into a usage forecast. Because heating fuel tracks how cold it is, dividing last winter’s fuel by that winter’s degree days gives a stable gallons-per-HDD rate for the building — then any HDD forecast (or a normal-year baseline) projects this winter’s need. It’s how oil dealers schedule automatic deliveries and how you budget a season without guessing. Recompute the rate after any efficiency upgrade.
Try it: interactive demo
Fuel per HDD and forecast HDD (price optional).
Variations
Fuel per HDD (calibrate)
From last season:
Season cost
Gallons × price:
Days to refill
Tank ÷ daily use:
Pitfalls & errors
Calibrate the rate. Use the building’s own fuel-per-HDD history.
Recompute after upgrades. New equipment changes the rate.
HDD base. Standard base is 65°F — be consistent.
Practice workbook
Frequently asked questions
How do I estimate fuel from degree days in Excel?
How do I find fuel per degree day?
What's a heating degree day?
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