When to use this calculator
Estimate input fuel energy for a useful-heating demand. Uses an entered efficiency compatible with the fuel-energy basis; heat pumps instead use COP.
Explore the electricity use & bills calculators for other questions in this topic. For a related calculation, use the LED Savings Calculator: Estimate energy savings from replacing equal-use lighting with lower-wattage bulbs.
PUTTING IT INTO PRACTICE
Heating Fuel Input: a worked example
The values below are an illustrative example, not a recommendation. Replace them with measurements or assumptions that match your question.
| Input | Example value |
|---|---|
| Useful heat required (kWh) | 100 |
| Overall conversion efficiency (%) | 80 |
| Result | 125 kWh input |
- Check the input labels and enter the example values above.
- Apply the relationship: Fuel input energy = useful heat/(efficiency/100).
- The result is 125 kWh input, rounded for display.
How to interpret your result
Uses an entered efficiency compatible with the fuel-energy basis; heat pumps instead use COP.
Watts describe power and kilowatt-hours describe energy. Fixed charges do not vary directly with consumption. Devices with thermostats or cycling loads need measured average energy or realistic operating time.
Frequently asked questions
Can I multiply rated watts by 24 hours for every appliance?
Only if it actually draws that power continuously. Cycling and variable-power appliances require a better average-use estimate.
When is the heating fuel input calculator useful?
Estimate input fuel energy for a useful-heating demand. Uses an entered efficiency compatible with the fuel-energy basis; heat pumps instead use COP.
How do I use the heating fuel input calculator?
Enter useful heat required (kwh), overall conversion efficiency (%). The result updates automatically. Use the units shown beside each input; the example values illustrate the method.
Which formula does this calculator use?
Fuel input energy = useful heat/(efficiency/100).
What should I check before using the result?
Uses an entered efficiency compatible with the fuel-energy basis; heat pumps instead use COP.
How are results rounded?
Scalar numbers display up to six decimal places, with scientific notation for very large or small values. Text, fraction, date and schedule outputs use the format described on the tool. Intermediate calculations use JavaScript floating-point arithmetic. Keep sensible precision for your measurements.
Calculators Map editorial process · Updated · Methods and limitations