Free · Energy scenarios
Three Building Heating Scenarios and Simple Payback
Compare three supplied construction and heating-demand scenarios using annual fuel costs and undiscounted additional-cost payback.
- Formula & worked example
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Calculator inputs
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How to use this calculator
- Enter the known values in the units shown. Results update as you type.
- Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
- Use the worked example to check the method. Reset restores the starting fields.
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Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.
Formula and method
A building cost ≈ 200000.00; A energy demand ≈ 11000.000; A heating cost ≈ 1100.0000; B building cost ≈ 218000.00; B savings ≈ 875.00000; B break even ≈ 20.571429; C building cost ≈ 230000.00; C savings ≈ 950.00000; C break even ≈ 31.578947.
Annual heat = area × supplied heat per area; annual gas = annual heat / gas energy per volume; incremental simple payback = additional construction cost / annual fuel savings.
Worked example
Enter these known values and leave the other values blank.
- Size
- 100 m²
- Gas price
- 1 USD /m³
- Gas to kwh
- 10 kWh/m³
- Construction cost
- 2000 USD / m²
- Energy demand
- 110 kWh/m²/ yrs
- Energy demand
- 22.5 kWh/m²/ yrs
- Energy demand
- 15 kWh/m²/ yrs
- Additional investment
- 9 %
- Additional investment
- 15 %
- Construction cost
- 200000 USD
- Heating cost
- 1100 USD / yrs
- Energy demand
- 11000 kWh/ yrs
- Gas usage
- 1100 m³/ yrs
- Construction cost
- 218000 USD
- Heating cost
- 225 USD / yrs
- Investment returns after
- 20.6 years
- Energy demand
- 2250 kWh/ yrs
- Gas usage
- 225 m³/ yrs
- Saving on heating
- 875 USD / yrs
- Construction cost
- 230000 USD
- Heating cost
- 150 USD / yrs
- Investment returns after
- 31.6 years
- Energy demand
- 1500 kWh/ yrs
- Gas usage
- 150 m³/ yrs
- Saving on heating
- 950 USD / yrs
Assumptions and limitations
- The three heat-demand values are editable scenario assumptions. The defaults are examples; they are not universal measurements for all buildings or climates.
- The 15 kWh/(m²·year) scenario corresponds to a familiar Passive House space-heating criterion, but this arithmetic alone does not certify a building or establish other requirements.
- Gas energy per cubic meter is supplied, and the model treats useful heat and supplied fuel energy equivalently. Account for heating-system efficiency in your demand or conversion assumptions.
- Annual savings are the reference fuel cost minus each alternative cost. Simple payback divides incremental construction expenditure by positive annual savings; it omits discounting, changes in tariffs, maintenance and residual value.
- Cost inputs are scenario values. Currency conversion choices retain the captured exchange snapshot, rather than live exchange rates; enter all costs in one currency for an internally consistent comparison.
- The calculation assumes the entered operating conditions are constant for the stated comparison period. It does not predict weather, site suitability, construction performance, taxes, financing or maintenance.
- Keep known inputs fixed with locks; clear the unknown before solving an inverse. Singularity or insufficient known inputs can leave results incomplete.
Common questions
Are the outputs a site-specific forecast?
No. They apply the stated algebraic model to supplied conditions. A real installation or building needs measured operating data and a broader engineering or cost assessment.
How are currency choices handled?
They use a fixed captured conversion snapshot. They do not retrieve current prices or exchange rates.
References
Bookify adds explicit model-domain checks: Construction expenditure per area cannot be negative. Additional investment cannot be negative. Supplied annual heating demand per area must be positive.