Energy Efficiency (EF/UEF) Savings Calculator
ANA›Life Services Authority›National Calculator Authority›Energy Efficiency (EF/UEF) Savings Calculator
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Energy Efficiency (EF/UEF) Savings Calculator
Estimate your annual energy and cost savings when upgrading from an old water heater to a more efficient model using Energy Factor (EF) or Uniform Energy Factor (UEF) ratings.
Fuel Type
Natural Gas Electric Propane (LP) Fuel Oil
Current Unit EF / UEF (old)
Typical old gas storage: 0.54–0.62 | Electric storage: 0.90–0.95 | Heat pump: 2.0–3.5
New Unit EF / UEF (upgrade)
Typical new gas condensing: 0.80–0.96 | Heat pump electric: 2.0–4.0 | Tankless gas: 0.82–0.96
Daily Hot Water Usage (gallons/day)
Average household: ~64 gal/day (DOE standard); adjust for your household size
Energy Rate ($/therm for gas)
Natural gas: ~$1.10–$1.50/therm | Electric: ~$0.12–$0.18/kWh | Propane: ~$2.50–$3.50/gallon | Oil: ~$3.50–$5.00/gallon
Cold Water Inlet Temperature (°F)
Typical groundwater: 50–65°F depending on region
Hot Water Setpoint Temperature (°F)
Recommended: 120°F (DOE); 140°F for dishwashers without internal heaters
Calculate Savings
function eneUpdateFuelLabel() { var fuel = document.getElementById("ene-fuel-type").value; var label = document.getElementById("ene-rate-label"); var hint = document.getElementById("ene-rate-hint"); var input = document.getElementById("ene-energy-rate"); if (fuel === "natural_gas") { label.textContent = "Energy Rate ($/therm)"; hint.textContent = "Natural gas: ~$1.10–$1.50/therm (1 therm = 100,000 BTU)"; input.placeholder = "e.g. 1.20"; } else if (fuel === "electric") { label.textContent = "Energy Rate ($/kWh)"; hint.textContent = "Electric: ~$0.12–$0.18/kWh (1 kWh = 3,412 BTU)"; input.placeholder = "e.g. 0.14"; } else if (fuel === "propane") { label.textContent = "Energy Rate ($/gallon propane)"; hint.textContent = "Propane: ~$2.50–$3.50/gallon (1 gallon propane = 91,502 BTU)"; input.placeholder = "e.g. 2.80"; } else if (fuel === "oil") { label.textContent = "Energy Rate ($/gallon fuel oil)"; hint.textContent = "Fuel oil: ~$3.50–$5.00/gallon (1 gallon #2 oil = 138,500 BTU)"; input.placeholder = "e.g. 4.00"; } }
function eneCalc() { var resultDiv = document.getElementById("ene-result");
// --- Read inputs --- var fuel = document.getElementById("ene-fuel-type").value; var oldEF = parseFloat(document.getElementById("ene-old-ef").value); var newEF = parseFloat(document.getElementById("ene-new-ef").value); var gallonsDay = parseFloat(document.getElementById("ene-daily-gallons").value); var rate = parseFloat(document.getElementById("ene-energy-rate").value); var tInlet = parseFloat(document.getElementById("ene-inlet-temp").value); var tOutlet = parseFloat(document.getElementById("ene-outlet-temp").value);
// --- Validation --- var errors = []; if (isNaN(oldEF) || oldEF 5) errors.push("Current EF/UEF must be between 0.01 and 5.0."); if (isNaN(newEF) || newEF 5) errors.push("New EF/UEF must be between 0.01 and 5.0."); if (isNaN(gallonsDay) || gallonsDay 80) errors.push("Inlet temperature must be between 35°F and 80°F."); if (isNaN(tOutlet) || tOutlet 160) errors.push("Outlet temperature must be between 90°F and 160°F."); if (!isNaN(tInlet) && !isNaN(tOutlet) && tOutlet 0) { resultDiv.innerHTML = "Please fix the following:" + errors.map(function(e){ return ""; }).join("") + ""; return; }
// --- Constants --- // BTU content per unit of fuel var btuPerUnit = { natural_gas: 100000, // 1 therm = 100,000 BTU electric: 3412, // 1 kWh = 3,412 BTU propane: 91502, // 1 gallon propane = 91,502 BTU oil: 138500 // 1 gallon #2 fuel oil = 138,500 BTU }; var fuelUnitLabel = { natural_gas: "therms", electric: "kWh", propane: "gallons", oil: "gallons" };
var BTU_PER_UNIT = btuPerUnit[fuel]; var UNIT_LABEL = fuelUnitLabel[fuel];
// Water heat capacity: 8.33 BTU per gallon per °F var BTU_PER_GAL_PER_DEG_F = 8.33;
// --- Core Formula --- // Annual BTU needed to heat water (useful energy demand): // Q_useful (BTU/yr) = gallons/day × 365 × 8.33 BTU/(gal·°F) × ΔT var deltaT = tOutlet - tInlet; var annualBTU = gallonsDay * 365 * BTU_PER_GAL_PER_DEG_F * deltaT;
// Annual energy INPUT required (fuel units/yr): // E_input = Q_useful / (EF × BTU_per_unit) // EF (Energy Factor) = useful energy output / total energy input var annualUnitsOld = annualBTU / (oldEF * BTU_PER_UNIT); var annualUnitsNew = annualBTU / (newEF * BTU_PER_UNIT);
// Annual energy savings (fuel units/yr): var annualUnitsSaved = annualUnitsOld - annualUnitsNew;
// Annual cost: var annualCostOld = annualUnitsOld * rate; var annualCostNew = annualUnitsNew * rate; var annualCostSaved = annualUnitsSaved * rate;
// Percentage improvement: var pctImprovement = ((newEF - oldEF) / oldEF) * 100; var pctCostSaved = (annualCostSaved / annualCostOld) * 100;
// 10-year and 15-year projections: var cost10yr = annualCostSaved * 10; var cost15yr = annualCostSaved * 15;
// CO2 emissions savings (approximate): // Natural gas: ~11.7 lbs CO2/therm | Electric: ~0.92 lbs CO2/kWh (US avg grid) | Propane: ~12.7 lbs/gal | Oil: ~22.4 lbs/gal var co2PerUnit = { natural_gas: 11.7, electric: 0.92, propane: 12.7, oil: 22.4 }; var annualCO2Saved = annualUnitsSaved * co2PerUnit[fuel]; // lbs/yr
// --- Format helpers --- function fmt(n, d) { return n.toLocaleString("en-US", {minimumFractionDigits: d, maximumFractionDigits: d}); } function fmtC(n) { return "$" + fmt(n, 2); }
resultDiv.innerHTML = "### Results " + "" + "MetricCurrent Unit (EF " + fmt(oldEF,2) + ")New Unit (EF " + fmt(newEF,2) + ")Savings" + "Annual Energy Input (" + UNIT_LABEL + "/yr)" + fmt(annualUnitsOld,1) + "" + fmt(annualUnitsNew,1) + "" + fmt(annualUnitsSaved,1) + " " + UNIT_LABEL + "" + "Annual Energy Cost" + fmtC(annualCostOld) + "" + fmtC(annualCostNew) + "" + fmtC(annualCostSaved) + " (" + fmt(pctCostSaved,1) + "%)" + "10-Year Cost Savings——" + fmtC(cost10yr) + "" + "15-Year Cost Savings——" + fmtC(cost15yr) + "" + "Annual CO₂ Reduction (approx.)——" + fmt(annualCO2Saved,0) + " lbs/yr" + "" + "Efficiency Improvement: " + fmt(pctImprovement,1) + "% more efficient
" + "Annual Useful Heat Demand: " + fmt(annualBTU/1000000,2) + " MMBTUs/yr " + "(based on " + fmt(gallonsDay,0) + " gal/day, ΔT = " + fmt(deltaT,0) + "°F)
"; }
#### Formulas Used
Annual Useful Heat Demand (BTU/yr):
Quseful = Gallons/day × 365 × 8.33 BTU/(gal·°F) × (Toutlet − Tinlet)
Annual Energy Input Required (fuel units/yr):
Einput = Quseful ÷ (EF × BTUper unit)
Annual Cost:
Cost = Einput × Rate ($/unit)
Annual Savings:
Savings = Costold − Costnew
Where EF (Energy Factor) or UEF (Uniform Energy Factor) = Useful Energy Output ÷ Total Energy Input over a standard test cycle.
#### Assumptions & References
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