Smart Thermostat Energy Savings Calculator

ANA›Life Services Authority›National Calculator Authority›Smart Thermostat Energy Savings Calculator

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Smart Thermostat Energy Savings Calculator

Estimate your annual energy and cost savings by switching to a smart thermostat. Based on DOE/EPA ENERGY STAR methodology using setback temperature differentials and occupancy schedules.

### Heating System

Average Monthly Heating Bill ($)

Heating Setback (°F reduction when away/asleep)

Recommended: 7–10°F for 8 hrs/day

Hours per Day at Setback Temperature

Heating Season (months/year)

### Cooling System

Average Monthly Cooling Bill ($)

Cooling Setback (°F increase when away/asleep)

Recommended: 4–7°F for 8 hrs/day

Hours per Day at Setback Temperature

Cooling Season (months/year)

### Smart Thermostat Details

Smart Thermostat Cost ($)

Installation Cost ($)

Utility Rebate / Tax Credit ($)

Calculate Savings

function smaCalc() { // --- Inputs --- var heatingBill = parseFloat(document.getElementById('sma-heating-bill').value); var heatingSetback = parseFloat(document.getElementById('sma-heating-setback').value); var heatingHours = parseFloat(document.getElementById('sma-heating-setback-hours').value); var heatingMonths = parseFloat(document.getElementById('sma-heating-months').value);

var coolingBill = parseFloat(document.getElementById('sma-cooling-bill').value); var coolingSetback = parseFloat(document.getElementById('sma-cooling-setback').value); var coolingHours = parseFloat(document.getElementById('sma-cooling-setback-hours').value); var coolingMonths = parseFloat(document.getElementById('sma-cooling-months').value);

var thermostatCost = parseFloat(document.getElementById('sma-thermostat-cost').value) || 0; var installationCost = parseFloat(document.getElementById('sma-installation-cost').value) || 0; var rebate = parseFloat(document.getElementById('sma-rebate').value) || 0;

var resultDiv = document.getElementById('sma-result');

// --- Validation --- var errors = []; if (isNaN(heatingBill) || heatingBill 24) errors.push("Heating setback hours must be between 0 and 24."); if (isNaN(heatingMonths) || heatingMonths 12) errors.push("Heating season must be between 1 and 12 months."); if (isNaN(coolingBill) || coolingBill 24) errors.push("Cooling setback hours must be between 0 and 24."); if (isNaN(coolingMonths) || coolingMonths 12) errors.push("Cooling season must be between 1 and 12 months.");

if (errors.length > 0) { resultDiv.style.display = 'block'; resultDiv.innerHTML = ''; return; }

// --- Core Formula --- // DOE methodology: each 1°F setback for 8 hours saves ~1% on heating/cooling costs. // Savings rate = (setback_degrees * setback_hours) / (24 * 100) // This is the fractional daily savings applied to the seasonal bill.

// Heating savings // savingsRate_heating = (heatingSetback * heatingHours) / (24 * 100) var heatingDailySavingsRate = (heatingSetback * heatingHours) / (24 * 100); // Cap at 30% (physical upper bound) heatingDailySavingsRate = Math.min(heatingDailySavingsRate, 0.30); var annualHeatingBill = heatingBill * heatingMonths; var annualHeatingSavings = annualHeatingBill * heatingDailySavingsRate;

// Cooling savings // Cooling is slightly less efficient per degree; apply a 0.85 efficiency factor var coolingEfficiencyFactor = 0.85; var coolingDailySavingsRate = (coolingSetback * coolingHours) / (24 * 100) * coolingEfficiencyFactor; coolingDailySavingsRate = Math.min(coolingDailySavingsRate, 0.30); var annualCoolingBill = coolingBill * coolingMonths; var annualCoolingSavings = annualCoolingBill * coolingDailySavingsRate;

// Total annual savings var totalAnnualSavings = annualHeatingSavings + annualCoolingSavings;

// Net investment var netInvestment = thermostatCost + installationCost - rebate; netInvestment = Math.max(netInvestment, 0);

// Payback period (years) var paybackYears = (totalAnnualSavings > 0) ? (netInvestment / totalAnnualSavings) : Infinity;

// 5-year and 10-year cumulative savings (net of investment) var savings5yr = (totalAnnualSavings * 5) - netInvestment; var savings10yr = (totalAnnualSavings * 10) - netInvestment;

// Percentage savings on total HVAC spend var totalAnnualHVAC = annualHeatingBill + annualCoolingBill; var pctSavings = (totalAnnualHVAC > 0) ? (totalAnnualSavings / totalAnnualHVAC * 100) : 0;

// --- Format helpers --- function fmt(n, dec) { dec = dec === undefined ? 2 : dec; return n.toLocaleString('en-US', {minimumFractionDigits: dec, maximumFractionDigits: dec}); } function fmtUSD(n) { return '$' + fmt(Math.abs(n)); }

var paybackStr = isFinite(paybackYears)
? fmt(paybackYears, 1) + ' years'
'N/A (no savings projected)';

// --- Output --- resultDiv.style.display = 'block'; resultDiv.innerHTML = '### Your Smart Thermostat Savings Estimate ' +

'' + 'MetricValue' + 'Annual Heating Savings' + fmtUSD(annualHeatingSavings) + '' + 'Annual Cooling Savings' + fmtUSD(annualCoolingSavings) + '' + 'Total Annual Savings' + fmtUSD(totalAnnualSavings) + '' + '% Savings on Total HVAC Bill' + fmt(pctSavings, 1) + '%' + 'Net Investment (after rebate)' + fmtUSD(netInvestment) + '' + 'Payback Period' + paybackStr + '' + '5-Year Net Savings' + (savings5yr >= 0 ? fmtUSD(savings5yr) : '-' + fmtUSD(savings5yr)) + '' + '10-Year Net Savings' + (savings10yr >= 0 ? fmtUSD(savings10yr) : '-' + fmtUSD(savings10yr)) + '' + '' +

'Results are estimates. Actual savings depend on climate, home insulation, HVAC efficiency, and usage habits.

'; }

#### Formulas Used

Heating Savings Rate (per day, as fraction of bill):

heating_savings_rate = (setback_°F × setback_hours) / (24 × 100) Based on the DOE rule of thumb: each 1°F setback for 8 hours ≈ 1% savings, generalized to any setback magnitude and duration.

Annual Heating Savings:

annual_heating_savings = monthly_heating_bill × heating_months × heating_savings_rate

Annual Cooling Savings (cooling is ~15% less responsive per degree due to latent heat loads):

cooling_savings_rate = (setback_°F × setback_hours) / (24 × 100) × 0.85 annual_cooling_savings = monthly_cooling_bill × cooling_months × cooling_savings_rate

Net Investment & Payback:

net_investment = thermostat_cost + installation_cost − rebate payback_years = net_investment / total_annual_savings savings_N_years = (total_annual_savings × N) − net_investment

#### Assumptions & References

More Calculators

References

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