Double Glazing Condensation Risk Calculator
ANA›Life Services Authority›National Calculator Authority›Double Glazing Condensation Risk 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; } }
Double Glazing Condensation Risk Calculator
Assess the risk of condensation forming on the inner pane of double glazing by comparing the inner glass surface temperature to the indoor dew point temperature.
Indoor Air Temperature (°C)
Indoor Relative Humidity (%)
Outdoor Air Temperature (°C)
Window U-Value (W/m²·K)
Typical double glazing: 1.2–2.8 W/m²·K; single glazing: ~5.6 W/m²·K
Indoor Surface Heat Transfer Coefficient (W/m²·K)
Typical still-air indoor value: 7.7–8 W/m²·K (ISO 6946)
Calculate Results will appear here.
function douCalc() { var Ti = parseFloat(document.getElementById('dou-indoor-temp').value); var RH = parseFloat(document.getElementById('dou-indoor-rh').value); var To = parseFloat(document.getElementById('dou-outdoor-temp').value); var U = parseFloat(document.getElementById('dou-u-value').value); var hi = parseFloat(document.getElementById('dou-hi').value);
// --- Input validation --- var errors = []; if (isNaN(Ti) || Ti 50) errors.push("Indoor temperature must be between -10 and 50 °C."); if (isNaN(RH) || RH 100) errors.push("Relative humidity must be between 1 and 100 %."); if (isNaN(To) || To 40) errors.push("Outdoor temperature must be between -30 and 40 °C."); if (isNaN(U) || U 6.0) errors.push("U-value must be between 0.5 and 6.0 W/m²·K."); if (isNaN(hi) || hi 25) errors.push("Indoor surface heat transfer coefficient must be between 2 and 25 W/m²·K."); if (Ti 0) { resDiv.innerHTML = 'Input Error:' + errors.map(function(e){ return ''; }).join('') + ''; return; }
// --- 1. Dew Point Temperature (Magnus formula) --- // Td = (243.04 * [ln(RH/100) + (17.625Ti)/(243.04+Ti)]) / // (17.625 - [ln(RH/100) + (17.625Ti)/(243.04+Ti)]) var a = 17.625; var b = 243.04; // °C var alpha = Math.log(RH / 100.0) + (a * Ti) / (b + Ti); var Td = (b * alpha) / (a - alpha);
// --- 2. Inner Glass Surface Temperature --- // Heat flux through window: q = U * (Ti - To) // Temperature drop from indoor air to inner glass surface: dT = q / hi = U(Ti-To)/hi // Inner glass surface temperature: Tg = Ti - U(Ti - To)/hi var q = U * (Ti - To); // W/m² var Tg = Ti - (q / hi); // °C
// --- 3. Temperature Factor (fRsi) --- // fRsi = (Tg - To) / (Ti - To) — dimensionless, per ISO 13788 var fRsi = (Tg - To) / (Ti - To);
// --- 4. Condensation Risk --- var margin = Tg - Td; // positive = safe, negative = condensation risk var risk, riskColor, riskDetail; if (margin >= 3) { risk = "Low Risk"; riskColor = "#2e7d32"; riskDetail = "The inner glass surface temperature is well above the dew point. Condensation is unlikely under these conditions."; } else if (margin >= 0) { risk = "Moderate Risk"; riskColor = "#f57c00"; riskDetail = "The inner glass surface temperature is close to the dew point. Condensation may occur if conditions worsen (e.g., higher humidity or lower outdoor temperature)."; } else { risk = "High Risk — Condensation Expected"; riskColor = "#c62828"; riskDetail = "The inner glass surface temperature is below the dew point. Condensation will form on the inner pane under these conditions."; }
// --- 5. Saturation vapour pressure & absolute humidity (informational) --- // Buck equation: es(T) = 0.61121 * exp((18.678 - T/234.5) * T/(257.14 + T)) [kPa] function es(T) { return 0.61121 * Math.exp((18.678 - T / 234.5) * (T / (257.14 + T))); } var es_indoor = es(Ti); // kPa var ea_indoor = (RH / 100) * es_indoor; // actual vapour pressure kPa var AH = (1000 * ea_indoor) / (0.4615 * (Ti + 273.15)); // g/m³ (ρv = pv/(Rv*T))
resDiv.innerHTML = '### Condensation Risk: ' + risk + ' ' + '' + 'Indoor Dew Point Temperature' + Td.toFixed(2) + ' °C' + 'Inner Glass Surface Temperature' + Tg.toFixed(2) + ' °C' + 'Temperature Margin (Tg − Td)' + margin.toFixed(2) + ' °C' + 'Temperature Factor fRsi' + fRsi.toFixed(3) + '' + 'Heat Flux Through Window' + q.toFixed(1) + ' W/m²' + 'Indoor Vapour Pressure' + (ea_indoor * 1000).toFixed(1) + ' Pa' + 'Indoor Absolute Humidity' + AH.toFixed(2) + ' g/m³' + '' + '' + riskDetail + '
'; }
#### Formulas Used
1. Dew Point Temperature — Magnus Formula (Lawrence 2005):
α = ln(RH/100) + (17.625 × Ti) / (243.04 + Ti) Td = 243.04 × α / (17.625 − α)
2. Inner Glass Surface Temperature:
q = U × (Ti − To) [W/m²] Tg = Ti − q / hi [°C]
Where U is the overall window U-value and hi is the indoor convective/radiative surface coefficient.
3. Temperature Factor (ISO 13788):
fRsi = (Tg − To) / (Ti − To)
A higher fRsi (closer to 1) indicates better thermal performance and lower condensation risk. ISO 13788 recommends fRsi ≥ 0.75 for most climates.
4. Condensation Risk Decision:
Margin = Tg − Td Margin ≥ 3 °C → Low Risk 0 ≤ Margin < 3 °C → Moderate Risk Margin < 0 °C → High Risk (condensation expected)
#### Assumptions & References
- Indoor surface heat transfer coefficient hi = 8 W/m²·K is the default per ISO 6946 (combined convection + radiation, still air).
- Lawrence, M.G. (2005). The relationship between relative humidity and the dew point temperature. Bulletin of the American Meteorological Society, 86(2), 225–233.
More Calculators
- Moisture and Rot Damage Assessment Calculator
- Snow Accumulation & Volume Calculator
- Smart Lighting Payback and ROI Calculator
- Wire Overload Heat Calculator
- Sprinkler Head Flow Rate & Coverage Calculator
- Snow Removal Time Estimator
- Pool Fence Compliance Calculator
- Pressure Washer Cleaning Unit Calculator
- Cleaning Service Cost Estimator
- Carpet Cleaning Cost Calculator
- Mortgage Payment Calculator
Read Next
Study Time Planner Authority Network America › Life Services Authority › National Calculator Authority .calc-container { max-width: 640px;...