Attic Air Sealing Heat Loss Calculator
ANA›Life Services Authority›National Calculator Authority›Attic Air Sealing Heat Loss Calculator
.calc-container { max-width: 640px; margin: 2rem 0; padding: 1.5rem; background: #fff; border: 1px solid #ddd; border-radius: 8px; box-shadow: 0 1px 3px rgba(0,0,0,0.06); font-family: system-ui, -apple-system, sans-serif; } .calc-container h3 { font-family: Georgia, serif; font-size: 1.15rem; color: #1a1a1a; margin-bottom: 1rem; padding-bottom: 0.5rem; border-bottom: 2px solid var(--ac, #3d5a80); } .calc-row { display: flex; align-items: center; gap: 0.75rem; margin-bottom: 0.75rem; flex-wrap: wrap; } .calc-row label { min-width: 160px; font-size: 0.9rem; color: #333; font-weight: 500; } .calc-row input[type="number"], .calc-row select { flex: 1; min-width: 120px; max-width: 200px; padding: 0.5rem 0.6rem; border: 1px solid #ccc; border-radius: 4px; font-size: 0.9rem; font-family: system-ui, sans-serif; color: #1a1a1a; background: #fafaf8; } .calc-row input:focus, .calc-row select:focus { outline: none; border-color: var(--ac, #3d5a80); box-shadow: 0 0 0 2px rgba(26,74,138,0.12); } .calc-row .unit { font-size: 0.82rem; color: #888; min-width: 30px; } .calc-btn { display: inline-block; margin-top: 0.5rem; padding: 0.55rem 1.5rem; background: var(--ac, #3d5a80); color: #fff; border: none; border-radius: 4px; font-size: 0.9rem; font-weight: 600; cursor: pointer; font-family: system-ui, sans-serif; } .calc-btn:hover { opacity: 0.9; } .calc-result { margin-top: 1.25rem; padding: 1rem 1.25rem; background: #f0f6fc; border-left: 3px solid var(--ac, #3d5a80); border-radius: 0 6px 6px 0; display: none; } .calc-result.visible { display: block; } .calc-result-label { font-size: 0.78rem; text-transform: uppercase; letter-spacing: 0.06em; color: #666; margin-bottom: 0.25rem; } .calc-result-value { font-size: 1.6rem; font-weight: 700; color: var(--ac, #3d5a80); } .calc-result-detail { font-size: 0.85rem; color: #555; margin-top: 0.5rem; line-height: 1.5; } .calc-note { margin-top: 1rem; font-size: 0.8rem; color: #888; font-style: italic; } .calc-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 0.75rem; margin-top: 0.75rem; } .calc-grid-item { padding: 0.6rem 0.8rem; background: #f8f9fa; border-radius: 4px; border: 1px solid #eee; } .calc-grid-item .label { font-size: 0.75rem; color: #888; text-transform: uppercase; letter-spacing: 0.04em; } .calc-grid-item .value { font-size: 1.1rem; font-weight: 600; color: #1a1a1a; } @media (max-width: 720px) { .calc-row { flex-direction: column; align-items: flex-start; gap: 0.3rem; } .calc-row label { min-width: auto; } .calc-row input[type="number"], .calc-row select { max-width: 100%; width: 100%; } .calc-grid { grid-template-columns: 1fr; } } .calc-chart { margin: 1rem 0; text-align: center; } .calc-chart svg { max-width: 100%; height: auto; } .calc-chart-legend { display: flex; flex-wrap: wrap; justify-content: center; gap: 0.6rem 1.2rem; margin-top: 0.6rem; font-size: 0.8rem; color: #555; } .calc-chart-legend span { display: inline-flex; align-items: center; gap: 0.3rem; } .calc-chart-legend i { display: inline-block; width: 10px; height: 10px; border-radius: 2px; font-style: normal; } .calc-related { max-width: 640px; margin: 2rem 0 1rem; padding: 1.25rem 1.5rem; background: #f8f9fa; border: 1px solid #e8e8e8; border-radius: 8px; } .calc-related h3 { font-family: Georgia, serif; font-size: 1rem; color: #1a1a1a; margin: 0 0 0.75rem; padding-bottom: 0.4rem; border-bottom: 2px solid var(--ac, #3d5a80); } .calc-related-list { list-style: none; padding: 0; margin: 0 0 0.75rem; display: grid; grid-template-columns: 1fr 1fr; gap: 0.4rem 1.5rem; } .calc-related-list li a { font-size: 0.88rem; color: var(--ac, #3d5a80); text-decoration: none; } .calc-related-list li a:hover { text-decoration: underline; } .calc-browse-all { margin: 0.5rem 0 0; font-size: 0.9rem; font-weight: 600; } .calc-browse-all a { color: var(--ac, #3d5a80); text-decoration: none; } .calc-browse-all a:hover { text-decoration: underline; } @media (max-width: 720px) { .calc-related-list { grid-template-columns: 1fr; } }
Attic Air Sealing Heat Loss Calculator
Estimate the heat loss through attic air leakage and the potential energy savings from proper air sealing, based on your home's characteristics and local climate.
Attic Floor Area (sq ft)
Current Air Changes per Hour (ACH) at 50 Pa
Typical leaky home: 8–15 ACH50. Tight home: 1–3 ACH50.
Post-Sealing ACH50 (target)
Recommended target: 3–5 ACH50 for existing homes.
Average Ceiling Height (ft)
Heating Degree Days (HDD, base 65°F)
Find your local HDD at NOAA or energystar.gov. Example: Chicago ≈ 6500, Atlanta ≈ 2800.
Energy Cost ($ per therm or per 100,000 BTU)
Natural gas: ~$1.00–$2.00/therm. Electric heat: convert kWh cost accordingly.
Heating System Efficiency (AFUE or COP, decimal)
Gas furnace: 0.80–0.97. Heat pump COP: 2.0–4.0.
Calculate Heat Loss & Savings
function attCalc() { // --- Grab inputs --- const floorArea = parseFloat(document.getElementById('att-floor-area').value); const ach50 = parseFloat(document.getElementById('att-ach').value); const ach50Sealed = parseFloat(document.getElementById('att-ach-sealed').value); const ceilHeight = parseFloat(document.getElementById('att-ceiling-height').value); const hdd = parseFloat(document.getElementById('att-hdd').value); const energyCost = parseFloat(document.getElementById('att-energy-cost').value); const furnaceEff = parseFloat(document.getElementById('att-furnace-eff').value);
// --- Validation --- const errors = []; if (isNaN(floorArea) || floorArea 10000) errors.push("Attic floor area must be between 100 and 10,000 sq ft."); if (isNaN(ach50) || ach50 30) errors.push("Current ACH50 must be between 0.5 and 30."); if (isNaN(ach50Sealed) || ach50Sealed 20) errors.push("Post-sealing ACH50 must be between 0.5 and 20."); if (!isNaN(ach50) && !isNaN(ach50Sealed) && ach50Sealed >= ach50) errors.push("Post-sealing ACH50 must be less than current ACH50."); if (isNaN(ceilHeight) || ceilHeight 20) errors.push("Ceiling height must be between 6 and 20 ft."); if (isNaN(hdd) || hdd 20000) errors.push("Heating degree days must be between 100 and 20,000."); if (isNaN(energyCost) || energyCost 10) errors.push("Energy cost must be between $0.10 and $10.00."); if (isNaN(furnaceEff) || furnaceEff 5.00) errors.push("Heating efficiency must be between 0.50 and 5.00.");
const resultDiv = document.getElementById('att-result'); if (errors.length > 0) { resultDiv.style.display = 'block'; resultDiv.innerHTML = 'Please fix the following:' + errors.map(e => '').join('') + ''; return; }
// --------------------------------------------------------------- // CORE FORMULAS // --------------------------------------------------------------- // 1. House volume (cubic feet) // V = floor_area × ceiling_height const houseVolume = floorArea * ceilHeight; // ft³
// 2. Natural Air Changes per Hour (ACHn) from blower-door ACH50 // ACHn = ACH50 / N where N ≈ 20 (LBL factor for average shielding/height) // Reference: Lawrence Berkeley National Laboratory infiltration model const N = 20; const achn_before = ach50 / N; // natural ACH before sealing const achn_after = ach50Sealed / N; // natural ACH after sealing
// 3. Infiltration airflow (CFM natural) // Q (ft³/min) = ACHn × V / 60 const cfm_before = (achn_before * houseVolume) / 60; const cfm_after = (achn_after * houseVolume) / 60; const cfm_saved = cfm_before - cfm_after;
// 4. Heat loss rate due to infiltration (BTU/hr per °F ΔT) // Q_loss = 1.1 × CFM (standard air heat capacity: 0.018 BTU/ft³·°F × 60 min/hr ≈ 1.08 ≈ 1.1) // Reference: ASHRAE Fundamentals Handbook const heatLossRate_before = 1.1 * cfm_before; // BTU/hr/°F const heatLossRate_after = 1.1 * cfm_after; const heatLossRate_saved = 1.1 * cfm_saved;
// 5. Annual heat loss (BTU/year) // Annual BTU = Q_loss_rate × HDD × 24 // HDD is in °F·days, multiply by 24 hr/day to get °F·hours const annualBTU_before = heatLossRate_before * hdd * 24; const annualBTU_after = heatLossRate_after * hdd * 24; const annualBTU_saved = heatLossRate_saved * hdd * 24;
// 6. Therms equivalent (1 therm = 100,000 BTU) const therms_before = annualBTU_before / 100000; const therms_after = annualBTU_after / 100000; const therms_saved = annualBTU_saved / 100000;
// 7. Delivered energy cost (account for furnace efficiency) // Cost = (therms × energy_cost) / efficiency const cost_before = (therms_before * energyCost) / furnaceEff; const cost_after = (therms_after * energyCost) / furnaceEff; const cost_saved = (therms_saved * energyCost) / furnaceEff;
// 8. Percent reduction const pctReduction = ((cost_before - cost_after) / cost_before) * 100;
// 9. Simple payback (assume typical air sealing cost $0.10–$0.25/sq ft → use $0.15 midpoint) // User can adjust; we show estimate const sealingCostPerSqFt = 0.15; const estimatedSealingCost = floorArea * sealingCostPerSqFt; const simplePayback = cost_saved > 0 ? estimatedSealingCost / cost_saved : Infinity;
// --------------------------------------------------------------- // FORMAT OUTPUT // --------------------------------------------------------------- function fmt(n, dec=0) { return n.toLocaleString('en-US', {minimumFractionDigits: dec, maximumFractionDigits: dec}); } function fmtC(n) { return '$' + n.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2}); }
resultDiv.style.display = 'block'; resultDiv.innerHTML = ` ### Results
MetricBefore SealingAfter SealingSavings
Natural ACH (ACHn)${achn_before.toFixed(3)}${achn_after.toFixed(3)}${(achn_before - achn_after).toFixed(3)} Infiltration Airflow (CFM)${fmt(cfm_before,1)}${fmt(cfm_after,1)}${fmt(cfm_saved,1)} Heat Loss Rate (BTU/hr/°F)${fmt(heatLossRate_before,1)}${fmt(heatLossRate_after,1)}${fmt(heatLossRate_saved,1)} Annual Heat Loss (BTU)${fmt(annualBTU_before)}${fmt(annualBTU_after)}${fmt(annualBTU_saved)} Annual Energy (therms equiv.)${fmt(therms_before,1)}${fmt(therms_after,1)}${fmt(therms_saved,1)} Annual Heating Cost${fmtC(cost_before)}${fmtC(cost_after)}${fmtC(cost_saved)}
🔥 Annual Cost Savings: ${fmtC(cost_saved)} | ${fmt(pctReduction,1)}% reduction in infiltration heating costs.
🏠 Estimated Sealing Cost: ${fmtC(estimatedSealingCost)} (at $0.15/sq ft — professional DIY range: $0.10–$0.25/sq ft)
📅 Simple Payback: ${simplePayback `; }
#### Formulas Used
1. House Volume: V = Floor Area × Ceiling Height (ft³)
2. Natural ACH (LBL Model): ACHn = ACH50 ÷ N, where N = 20 (average shielding, 1-story equivalent)
3. Infiltration Airflow: CFM = (ACHn × V) ÷ 60
4. Sensible Heat Loss Rate: Q̇ = 1.1 × CFM (BTU/hr per °F ΔT) — from air heat capacity 0.018 BTU/ft³·°F × 60 min/hr
5. Annual Heat Loss: BTU/yr = Q̇ × HDD × 24 hr/day
6. Annual Energy: Therms = Annual BTU ÷ 100,000
7. Annual Cost: Cost = (Therms × $/therm) ÷ Efficiency (AFUE or COP)
8. Simple Payback: Years = Sealing Cost ÷ Annual Savings
#### Assumptions & References
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