United States version
How it works
Compare the fuel-cost consequence of two seasonal efficiencies at the same useful heating load.
This is the United States planning view, with monetary inputs and outputs in USD. A currency label does not establish that a tax rate, construction price, coverage rule or legal limit has been verified locally. The inputs and limitations below describe the actual scope.
Input query strings and outputs
Use an input name in this page’s URL as ?name=value, and join additional inputs with &. Portable shared links may instead use the compact ?ac= state parameter.
Input query strings
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?annualFuelCost=Current annual fuel-only costMoney · Required · Default: 1,800
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?oldEfficiency=Current seasonal efficiencyPercentage · Required · Default: 75
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?newEfficiency=Replacement seasonal efficiencyPercentage · Required · Default: 95
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?projectCost=Installed replacement priceMoney · Required · Default: 7,000
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?incentive=Confirmed incentiveMoney · Required · Default: 0
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?maintenanceChange=Additional annual maintenanceMoney · Required · Default: 0
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?years=Planning horizon, yearsNumber · Required · Default: 15
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?discountRate=Discount ratePercentage · Required · Default: 4
Outputs
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capitalNet capital costCurrency · Currency: USD
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annualSavingFirst-year net savingCurrency · Currency: USD
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paybackSimple payback, yearsNumber · Primary output
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npvDiscounted net valueCurrency · Currency: USD
Formula
gross fuel saving = current fuel spending × (1 − old efficiency ÷ new efficiency).
Calculations retain numeric precision internally. Displayed values are rounded for readability. Quantities that must be purchased as whole units are rounded up only where the formula explicitly requires it.
Read the inputs before calculating
- Current annual fuel-only cost: Enter the quantity described by the label.
- Current seasonal efficiency: Enter the quantity described by the label.
- Replacement seasonal efficiency: Enter the quantity described by the label.
- Installed replacement price: Enter the quantity described by the label.
- Confirmed incentive: Enter the quantity described by the label.
- Additional annual maintenance: Enter the quantity described by the label.
- Planning horizon, years: Enter the quantity described by the label.
- Discount rate: Enter the quantity described by the label.
Reproducible worked example
The following is a fictional arithmetic example, not a local quote, a verified claimant or a market forecast. Its values are included so the formula can be checked. The form does not automatically confirm any verification checkbox.
| Input | Example value |
|---|---|
| Current annual fuel-only cost | 1,800 |
| Current seasonal efficiency | 75 |
| Replacement seasonal efficiency | 95 |
| Installed replacement price | 7,000 |
| Confirmed incentive | 0 |
| Additional annual maintenance | 0 |
| Planning horizon, years | 15 |
| Discount rate | 4 |
| Output | Calculated result |
|---|---|
| Net capital cost | USD 7,000 |
| First-year net saving | USD 378.9474 |
| Simple payback, years | 18.4722 |
| Discounted net value | USD -2,786.7163 |
Interpreting a changed assumption
Start with one complete scenario and change only one input when diagnosing a difference. Recheck units, the period of every rate, whether an amount is recurring or one-off, and whether a cost is already included elsewhere. A larger calculated benefit is not evidence that an assumption is more likely to occur.
Limitations
- The formula holds useful heat demand constant and excludes changes in weather, thermostat use and duct losses. Fixed fuel charges are not fuel-only spending.
Frequently asked questions
What does this Furnace Replacement result represent?
Compare the fuel-cost consequence of two seasonal efficiencies at the same useful heating load. It applies the displayed formula to your inputs; it does not infer omitted facts.
Are the starting amounts verified United States prices or legal rules?
No. Numeric defaults are illustrative unless an input or dated reference explicitly identifies a researched component. Currency is USD; local quotes, eligibility and unsupported rules must be entered and verified separately.
What must I check before relying on the result?
Check the input units, supplier or authority evidence, the stated model exclusions and the period used for costs. This arithmetic does not supply missing site-specific design or local legal rules.
Can I compare or share different assumptions?
Change one assumption at a time and use the browser-local project or share controls. A shared URL contains the encoded input values; do not include information you do not wish to disclose.
Sources and reference scope
- DOE energy-use arithmetic — retrieved 2026-09-24. Energy consumption versus power; not a local tariff or an approval of this implementation.
- PVWatts: site-specific solar estimation — retrieved 2026-09-24. External site-yield model. AskCalculators uses your entered yield; it does not call or reproduce PVWatts.
- DOE insulation overview — retrieved 2026-09-24. Insulation and thermal resistance concepts; not structural or code approval.
These references support only their stated scope. They are not evidence that every local rule or price needed by the master expansion has been loaded.