Useful Heating Cost Calculator

How the useful heating cost calculator works

Required fuel input kWh = useful output kWh ÷ annual efficiency fraction. Metered fuel units = input kWh ÷ input kWh per matching fuel unit. Efficiency must be positive and at most 100% on the stated output/input basis; heat-pump COP belongs in a different model.

Fuel cost extends the unrounded calculated metered units at the entered price and rounds half-up to cents. Add the separately rounded annual fixed cost. Cost per useful kWh divides that rounded total by useful heat. At zero useful demand, fuel use is zero, fixed cost remains and the unit-cost ratio is unavailable.

Fuel is continuously metered in this model; no whole package or delivery increment is applied. Keep annual performance, fuel heat content and system boundaries consistent. Auxiliary electricity, distribution losses outside the entered efficiency, capital cost, maintenance not entered, taxes and financing are excluded. DOE explains annual boiler output/input efficiency; it does not supply the illustrative values here.

Worked example

10,000 kWh useful heat at 85% annual efficiency requires about 11,764.706 kWh fuel input. At 10 kWh per metered unit this is about 1,176.471 units. A price of 1/unit rounds fuel cost to 1,176.47; adding 100 annual fixed cost totals 1,276.47. At 100% entered efficiency, fuel cost is 1,000 and total is 1,100.

Sources and assumptions

The source material explains the underlying calculation or pricing structure. Entered prices, costs, schedules and scenario choices are your assumptions; this tool does not obtain supplier quotes or predict actual results.

• U.S. DOE: boiler energy efficiency and energy-cost calculations
• EIA: energy units, heat content and conversion calculators