Calculate a heating K factor (degree days per gallon of heating oil) from degree days and fuel used, or estimate fuel use or degree days from K.
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Heating K Factor Formula
The heating K factor is the number of heating degree days covered by one unit of fuel. This calculator uses heating degree days, fuel used, and the heating K factor. It converts all inputs to base units first: °F·day for heating degree days and U.S. liquid gallons for fuel.
- K = heating K factor, usually expressed as °F·day/gal
- HDD = heating degree days over the period
- F = fuel used over the same period
Choose the quantity to calculate, enter the two known quantities and select Calculate. The formulas above apply after unit conversion.
The selected unit matters. For example, °C·day values are converted to °F·day, and liters are converted to gallons before the formula is applied.
Heating K Factor Unit Conversions
These are the unit conversions used to keep the calculation consistent.
| Quantity | Input Unit | Base Unit Conversion |
|---|---|---|
| Heating degree days | °F·day | 1 °F·day = 1 °F·day |
| Heating degree days | °C·day | 1 °C·day = 1.8 °F·day |
| Fuel used | Gallons | 1 gallon = 1 gallon |
| Fuel used | Liters | 1 liter ≈ 0.264172 U.S. gallons |
How to Read a Heating K Factor
| K Factor Pattern | General Meaning |
|---|---|
| Higher K factor | More heating degree days per gallon or liter of fuel. This usually means lower fuel use for the same weather conditions. |
| Lower K factor | Fewer heating degree days per unit of fuel. This may indicate higher fuel use, colder indoor settings, equipment issues, or building heat loss. |
| Sudden change from past values | Check for changes in fuel delivery records, thermostat settings, occupancy, boiler or furnace service, or the HDD base temperature used. |
Example Heating K Factor Calculations
Example 1: Calculate heating K factor
You used 150 gallons of fuel during a period with 3,600 heating degree days.
The heating K factor is 24 °F·day/gal.
Example 2: Calculate fuel used
Your heating K factor is 30 °F·day/gal, and the period has 4,500 heating degree days.
The estimated fuel used is 150 gallons.
Heating K Factor FAQ
What does a heating K factor tell you?
A heating K factor tells you how many heating degree days you get from one unit of fuel. For example, a K factor of 25 °F·day/gal means each gallon of fuel corresponds to 25 heating degree days for the period measured.
Is a higher heating K factor better?
In general, yes. A higher K factor means less fuel is being used for the same amount of heating demand. However, you should compare the same building over similar operating conditions. Thermostat changes, insulation, burner efficiency, hot water use, and occupancy can all affect the result.
Can I mix Celsius, Fahrenheit, gallons, and liters?
Yes, but the units must be converted before applying the formula. The calculator does this automatically. If calculating by hand, convert °C·day to °F·day by multiplying by 1.8, and convert liters to U.S. gallons by dividing by 3.785411784.
