HVAC System Payback Period Calculator — Upfront Cost vs. Long-Term Savings
ANA›Life Services Authority›National Calculator Authority›HVAC System Payback Period Calculator — Upfront Cost vs. Long-Term Savings
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HVAC System Payback Period Calculator — Upfront Cost vs. Long-Term Savings
Enter your current system's efficiency, the new system's efficiency, your energy costs, and installation details to find out exactly when your investment breaks even — and how much you'll save over time.
New HVAC System Total Cost (installation included) ($)
Rebates / Tax Credits ($)
Existing System Efficiency (SEER / HSPF / AFUE %)
New System Efficiency (SEER / HSPF / AFUE %)
Current Annual Energy Bill for HVAC ($)
Annual Energy Cost Inflation Rate (%)
Current Annual Maintenance / Repair Cost ($)
New System Annual Maintenance Cost ($)
Analysis Period (years)
Calculate Payback Period
function hvaCalc() { // --- gather inputs --- var newCost = parseFloat(document.getElementById('hva-new-cost').value); var rebate = parseFloat(document.getElementById('hva-rebate').value) || 0; var oldSeer = parseFloat(document.getElementById('hva-old-seer').value); var newSeer = parseFloat(document.getElementById('hva-new-seer').value); var annualEnergy = parseFloat(document.getElementById('hva-annual-energy').value); var inflation = parseFloat(document.getElementById('hva-energy-inflation').value) || 0; var maintOld = parseFloat(document.getElementById('hva-maintenance-old').value) || 0; var maintNew = parseFloat(document.getElementById('hva-maintenance-new').value) || 0; var years = parseInt(document.getElementById('hva-analysis-years').value) || 15;
var resultDiv = document.getElementById('hva-result');
// --- validation --- var errors = []; if (isNaN(newCost) || newCost = newCost) errors.push('Rebates/credits cannot exceed or equal the total system cost.'); if (inflation 20) errors.push('Energy inflation rate must be between 0% and 20%.'); if (years 30) errors.push('Analysis period must be between 1 and 30 years.');
if (errors.length > 0) { resultDiv.innerHTML = 'Please fix the following:' + errors.map(function(e){ return ''; }).join('') + ''; return; }
// --- core calculations --- // Net upfront investment after rebates var netCost = newCost - rebate;
// Efficiency improvement ratio var efficiencyRatio = oldSeer / newSeer; // fraction of old energy use retained
// Year-1 energy savings from efficiency improvement // New energy cost = annualEnergy * (oldSeer / newSeer) // Savings = annualEnergy - annualEnergy * (oldSeer / newSeer) var year1EnergySavings = annualEnergy * (1 - efficiencyRatio);
// Year-1 maintenance savings var year1MaintSavings = maintOld - maintNew;
// Year-1 total savings var year1TotalSavings = year1EnergySavings + year1MaintSavings;
if (year1TotalSavings Annual savings are zero or negative with the values entered. ' + 'Verify that the new system is more efficient and/or has lower maintenance costs.'; return; }
// --- year-by-year cumulative savings (with inflation on energy portion) --- var inflationRate = inflation / 100; var cumulativeSavings = 0; var paybackYear = null; var paybackFraction = null; var tableRows = ''; var totalSavingsAtEnd = 0;
for (var y = 1; y = netCost) { paybackYear = y; // Linear interpolation within the year var deficit = netCost - prevCumulative; paybackFraction = deficit / totalSavingsThisYear; // fraction of year y needed }
var roi = ((cumulativeSavings - netCost) / netCost * 100).toFixed(1); tableRows += '' + '' + y + '' + '$' + energySavingsThisYear.toFixed(0) + '' + '$' + totalSavingsThisYear.toFixed(0) + '' + '$' + cumulativeSavings.toFixed(0) + '' + '' + roi + '%' + ''; }
totalSavingsAtEnd = cumulativeSavings; var netBenefit = totalSavingsAtEnd - netCost;
// Format payback period var paybackText; if (paybackYear === null) { paybackText = 'Not reached within ' + years + '-year analysis period'; } else { var fullYears = paybackYear - 1; var months = Math.round(paybackFraction * 12); if (months === 12) { fullYears += 1; months = 0; } paybackText = fullYears + ' year' + (fullYears !== 1 ? 's' : '') + (months > 0 ? ' and ' + months + ' month' + (months !== 1 ? 's' : '') : ''); }
// Simple payback (no inflation, for reference) var simplePayback = netCost / year1TotalSavings;
resultDiv.innerHTML = '### Results ' + '' + 'Net Upfront Investment' + '$' + netCost.toFixed(2) + '' + 'Year-1 Energy Savings' + '$' + year1EnergySavings.toFixed(2) + '' + 'Year-1 Maintenance Savings' + '$' + year1MaintSavings.toFixed(2) + '' + 'Year-1 Total Savings' + '$' + year1TotalSavings.toFixed(2) + '' + 'Simple Payback Period' + '' + simplePayback.toFixed(1) + ' yrs' + 'Inflation-Adjusted Payback' + '' + paybackText + '' + 'Total Savings Over ' + years + ' Years' + '$' + totalSavingsAtEnd.toFixed(2) + '' + 'Net Benefit After ' + years + ' Years' + '= 0 ? 'calc-positive' : 'calc-negative') + '">$' + netBenefit.toFixed(2) + '' + '' + '#### Year-by-Year Breakdown ' + '' + '' + 'YearEnergy SavingsTotal SavingsCumulative SavingsROI' + '' + tableRows + '' + ''; }
#### Formulas Used
Net Upfront Investment:
Net Cost = New System Cost − Rebates & Tax Credits
Efficiency Improvement Ratio:
Efficiency Ratio = Old SEER (or HSPF/AFUE) ÷ New SEER (or HSPF/AFUE)
Year-1 Annual Energy Savings:
Energy Savings (Yr 1) = Current Annual Energy Bill × (1 − Efficiency Ratio)
Year-1 Maintenance Savings:
Maintenance Savings (Yr 1) = Old Annual Maintenance Cost − New Annual Maintenance Cost
Total Savings in Year n (with energy inflation):
Total Savings (Yr n) = Energy Savings (Yr 1) × (1 + Inflation Rate)^(n−1) + Maintenance Savings (Yr 1)
Cumulative Savings after N years:
Cumulative Savings = Σ [Total Savings (Yr n)] for n = 1 to N
Simple Payback Period (no inflation):
Simple Payback = Net Cost ÷ Year-1 Total Savings
Inflation-Adjusted Payback: The year in which Cumulative Savings first equals or exceeds Net Cost, with linear interpolation within that year.
ROI in Year n:
ROI = (Cumulative Savings − Net Cost) ÷ Net Cost × 100%
#### Assumptions & References
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