Garage Ventilation and Exhaust Fan Sizing Calculator

ANA›Life Services Authority›National Calculator Authority›Garage Ventilation and Exhaust Fan Sizing 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; } }

Garage Ventilation and Exhaust Fan Sizing Calculator

Calculate the required exhaust fan size (CFM) for your garage based on dimensions, ceiling height, and usage type to ensure safe and adequate ventilation.

Garage Length (ft)

Garage Width (ft)

Ceiling Height (ft)

Air Changes per Hour (ACH)

Standard Residential (6 ACH) Active Use / Light Workshop (10 ACH) Heavy Use / Auto Repair (15 ACH) Custom ACH

Custom ACH Value

Number of Cars / Vehicles

Calculate

document.getElementById('gar-ach').addEventListener('change', function() { var customGroup = document.getElementById('gar-custom-ach-group'); customGroup.style.display = (this.value === 'custom') ? 'block' : 'none'; });

function garCalc() { var resultDiv = document.getElementById('gar-result'); resultDiv.style.display = 'none';

var length = parseFloat(document.getElementById('gar-length').value); var width = parseFloat(document.getElementById('gar-width').value); var height = parseFloat(document.getElementById('gar-height').value); var achSel = document.getElementById('gar-ach').value; var cars = parseInt(document.getElementById('gar-cars').value) || 0;

// Validation if (isNaN(length) || length Please enter a valid garage length.'; resultDiv.style.display = 'block'; return; } if (isNaN(width) || width Please enter a valid garage width.'; resultDiv.style.display = 'block'; return; } if (isNaN(height) || height 30) { resultDiv.innerHTML = 'Ceiling height must be between 6 and 30 ft.'; resultDiv.style.display = 'block'; return; }

var ach; if (achSel === 'custom') { ach = parseFloat(document.getElementById('gar-custom-ach').value); if (isNaN(ach) || ach 60) { resultDiv.innerHTML = 'Custom ACH must be between 1 and 60.'; resultDiv.style.display = 'block'; return; } } else { ach = parseFloat(achSel); }

if (cars 20) { resultDiv.innerHTML = 'Number of vehicles must be between 0 and 20.'; resultDiv.style.display = 'block'; return; }

// Core formula: CFM = (Volume × ACH) / 60 var volume = length * width * height; // cubic feet var cfmBase = (volume * ach) / 60.0; // CFM from ACH method

// Additional CFM allowance per vehicle (ASHRAE / ACGIH guidance: ~100 CFM per car for CO dilution) var cfmPerCar = 100.0; var cfmCars = cars * cfmPerCar;

// Required CFM is the greater of ACH-based or vehicle-based requirement var cfmRequired = Math.max(cfmBase, cfmCars);

// Add 20% safety/efficiency factor for duct losses and motor inefficiency var cfmDesign = cfmRequired * 1.20;

// Estimate number of air changes actually achieved with design CFM var achActual = (cfmDesign * 60.0) / volume;

// Rough fan power estimate: typical exhaust fans ~0.5–1.0 W per CFM; use 0.75 W/CFM var wattEstimate = cfmDesign * 0.75;

// Duct sizing: velocity ~500 FPM recommended for quiet operation // Area (ft²) = CFM / FPM → diameter (in) = sqrt(4 × Area / π) × 12 var ductVelocity = 500.0; // FPM var ductAreaFt2 = cfmDesign / ductVelocity; var ductDiamIn = Math.sqrt((4.0 * ductAreaFt2) / Math.PI) * 12.0;

// Round up duct diameter to nearest standard size var standardDucts = [4, 5, 6, 7, 8, 9, 10, 12, 14, 16, 18, 20]; var ductStd = standardDucts.find(function(d){ return d >= ductDiamIn; }) || Math.ceil(ductDiamIn);

resultDiv.innerHTML = '### Ventilation Results ' + '' + 'Garage Volume' + volume.toFixed(0) + ' ft³' + 'ACH Used' + ach.toFixed(1) + ' air changes/hr' + 'CFM (ACH Method)' + cfmBase.toFixed(0) + ' CFM' + 'CFM (Vehicle Method)' + cfmCars.toFixed(0) + ' CFM' + 'Required CFM (larger of two)' + cfmRequired.toFixed(0) + ' CFM' + 'Design CFM (with 20% factor)' + cfmDesign.toFixed(0) + ' CFM' + 'Actual ACH Achieved' + achActual.toFixed(1) + ' ACH' + 'Estimated Fan Power' + wattEstimate.toFixed(0) + ' W' + 'Calculated Duct Diameter' + ductDiamIn.toFixed(1) + ' in' + 'Recommended Standard Duct Size' + ductStd + ' in' + '' + 'Recommendation: Select an exhaust fan rated for at least ' + Math.ceil(cfmDesign / 10) * 10 + ' CFM with a ' + ductStd + '-inch duct connection.

';

resultDiv.style.display = 'block'; }

#### Formulas Used

1. Volume: V = Length × Width × Height (ft³)

2. ACH Method CFM: CFMACH = (V × ACH) ÷ 60

3. Vehicle Method CFM: CFMvehicles = Number of Cars × 100 CFM/car

4. Required CFM: CFMrequired = max(CFMACH, CFMvehicles)

5. Design CFM (with 20% safety factor): CFMdesign = CFMrequired × 1.20

6. Duct Diameter: d = √(4 × (CFMdesign ÷ 500 FPM) ÷ π) × 12 inches

7. Fan Power Estimate: W ≈ CFMdesign × 0.75 W/CFM

#### Assumptions & References

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References

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