Inputs
Example Data Table
| Scenario | Heat (kWh) | Current Eff. | New Eff. | Fuel (per kWh) | Net Cost | Year‑1 Savings | Payback |
|---|---|---|---|---|---|---|---|
| Example A | 18,000 | 78% | 92% | 0.10 | 4,000 | ~520 | ~8 yrs |
| Example B | 25,000 | 75% | 94% | 0.12 | 5,500 | ~980 | ~6 yrs |
Formula Used
Delivered heat demand is converted to fuel input using efficiency. Fuel input is priced, then maintenance is added to estimate yearly totals.
- Fuel input (kWh): FuelInput = HeatDemand ÷ (Efficiency% ÷ 100)
- Energy cost: EnergyCost = FuelInput × FuelCostPerKwh
- Annual total: AnnualTotal = EnergyCost + Maintenance
- Net cost: NetCapex = UpgradeCost − Grants
- NPV: NPV = −NetCapex + Σ( Benefit(y) ÷ (1+DiscountRate)^y )
- CO2 saved: (CurrentFuelInput − NewFuelInput) × CO2Factor
How to Use This Calculator
- Enter your annual heat demand in kWh.
- Set current and expected new efficiency values.
- Provide fuel cost per kWh of fuel input.
- Add current and future annual maintenance costs.
- Enter upgrade cost and any grants or incentives.
- Choose projection years, escalation, and discount rate.
- Optionally add emissions factor and carbon value.
- Press Calculate to see results above the form.
Energy baseline and input quality
Annual heat demand drives the model. A household using 18,000 kWh of delivered heat and paying 0.10 per kWh of fuel input will spend about 2,308 on fuel at 78% efficiency, before maintenance. If you only know annual fuel spend, divide by unit price to approximate input. Seasonal efficiency often differs from nameplate ratings. Metered usage, degree‑day normalized bills, or a recent audit improves confidence and prevents underestimating savings.
Efficiency upgrade and fuel reduction
The calculator converts delivered heat to fuel input by dividing by efficiency. Moving from 78% to 92% reduces fuel input by roughly 15%. For the 18,000 kWh example, fuel input falls from about 23,077 kWh to 19,565 kWh. The difference translates directly into lower annual energy cost when fuel pricing is stable.
Maintenance, incentives, and net cost
Real projects include service plans, repair risk, and rebates. If installed cost is 4,500 and incentives are 500, net cost is 4,000. When maintenance drops from 220 to 120 per year, an additional 100 is captured alongside energy savings. Net cost and recurring savings set the payback trajectory.
Projection assumptions and discounted value
Fuel and maintenance escalation rates apply yearly, while the discount rate converts future benefits into present value. With 3% fuel escalation and a 6% discount rate, later savings matter less than early savings, and NPV can remain negative if the upgrade cost is high. Sensitivity checks help. Adjust the analysis years to match expected equipment life.
Carbon impact and decision metrics
Emissions are estimated from fuel input using a factor such as 0.205 kg per kWh. The model reports tonnes saved and can apply a carbon value per tonne to reflect policy or internal targets. Use year‑1 savings, NPV, ROI, and both payback measures together to compare upgrade options consistently.
FAQs
What efficiency value should I use?
Use seasonal or real‑world efficiency if available. Nameplate ratings can overstate performance. If uncertain, use the latest service report, an audit estimate, or a conservative range and compare outcomes.
How do I estimate annual heat demand?
Start with fuel bills and local unit prices to estimate fuel input, then multiply by current efficiency to approximate delivered heat. Better options include smart‑meter data, degree‑day normalization, or an energy audit.
Why does the calculator include escalation rates?
Fuel and maintenance costs often change over time. Escalation rates let you stress‑test savings under rising or falling prices, producing a more realistic long‑term view than a single‑year snapshot.
What does NPV tell me here?
NPV converts future benefits to today’s value using the discount rate and subtracts net upgrade cost. A positive NPV indicates the upgrade returns more value than keeping the money at the chosen rate.
How is carbon savings estimated?
The tool estimates fuel input for both systems and multiplies the difference by your CO2 factor. It reports tonnes saved per year and can assign an optional monetary value per tonne for comparisons.
Can payback show “Not reached”?
Yes. If yearly benefits do not offset the net upgrade cost within the analysis years, payback remains unreached. Increase the analysis period, refine costs, or review assumptions like efficiency gain and fuel price.