Ventilation Rate Calculator (CFM & ACH)
.vent-calc-container {
max-width: 800px;
margin: 0 auto;
padding: 20px;
font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
background: #f9f9f9;
border: 1px solid #e0e0e0;
border-radius: 8px;
}
.vent-calc-header {
text-align: center;
margin-bottom: 30px;
}
.vent-calc-header h2 {
margin: 0;
color: #2c3e50;
}
.vent-row {
display: flex;
flex-wrap: wrap;
gap: 20px;
margin-bottom: 20px;
}
.vent-col {
flex: 1;
min-width: 200px;
}
.vent-input-group {
margin-bottom: 15px;
}
.vent-input-group label {
display: block;
margin-bottom: 5px;
font-weight: 600;
color: #444;
}
.vent-input-group input, .vent-input-group select {
width: 100%;
padding: 10px;
border: 1px solid #ccc;
border-radius: 4px;
font-size: 16px;
box-sizing: border-box;
}
.vent-input-group .unit {
font-size: 0.85em;
color: #666;
margin-top: 4px;
display: block;
}
.vent-btn {
display: block;
width: 100%;
padding: 15px;
background-color: #0073aa;
color: white;
border: none;
border-radius: 4px;
font-size: 18px;
font-weight: bold;
cursor: pointer;
transition: background 0.3s;
}
.vent-btn:hover {
background-color: #005177;
}
.vent-results {
margin-top: 30px;
padding: 20px;
background: #ffffff;
border-left: 5px solid #0073aa;
box-shadow: 0 2px 5px rgba(0,0,0,0.05);
display: none;
}
.vent-result-item {
margin-bottom: 15px;
border-bottom: 1px solid #eee;
padding-bottom: 10px;
display: flex;
justify-content: space-between;
align-items: center;
}
.vent-result-item:last-child {
border-bottom: none;
margin-bottom: 0;
}
.vent-result-label {
font-size: 16px;
color: #555;
}
.vent-result-value {
font-size: 20px;
font-weight: bold;
color: #2c3e50;
}
.ach-reference {
background: #eef7fb;
padding: 15px;
border-radius: 4px;
margin-top: 10px;
font-size: 0.9em;
}
.ach-reference h4 {
margin-top: 0;
margin-bottom: 10px;
color: #0073aa;
}
.ach-grid {
display: grid;
grid-template-columns: 1fr 1fr;
gap: 10px;
}
.vent-article {
margin-top: 40px;
line-height: 1.6;
color: #333;
}
.vent-article h3 {
color: #2c3e50;
border-bottom: 2px solid #eee;
padding-bottom: 10px;
margin-top: 30px;
}
.vent-article ul {
padding-left: 20px;
}
.vent-article li {
margin-bottom: 8px;
}
Room Dimensions
Length
feet
Width
feet
Ceiling Height
feet
Air Quality Targets
Target Air Changes per Hour (ACH)
Number of times air is replaced per hour
Common ACH Guidelines:
Residential (Basic): 0.35 – 1
Residential (Purifier): 4 – 6
Office Space: 4 – 6
Kitchen/Bath: 15 – 20
Medical/Lab: 6 – 12
Classroom: 3 – 4
Calculate Required Airflow
Calculation Results
Total Room Volume:
– ft³
Required Airflow (CFM):
– CFM
Required Airflow (Liters/sec):
– L/s
Air Turnover Time:
– minutes
Understanding Ventilation Rate Calculations
Proper ventilation is critical for maintaining Indoor Air Quality (IAQ), removing contaminants such as CO2, volatile organic compounds (VOCs), and airborne pathogens. This calculator helps HVAC technicians, facility managers, and homeowners determine the required fan size or system capacity needed to meet specific air exchange standards.
Key Metrics Explained
ACH (Air Changes per Hour): This metric indicates how many times the entire volume of air in a room is replaced or filtered within one hour. A higher ACH means better ventilation and cleaner air.CFM (Cubic Feet per Minute): This is the standard measurement for airflow in the United States. It represents the volume of air a fan or HVAC system moves every minute.Room Volume: The total amount of space in the room, calculated as Length × Width × Height.
The Ventilation Formula
To calculate the required airflow (CFM) to achieve a specific Air Change per Hour (ACH) rate, we use the following formula:
CFM = (Room Volume × Target ACH) / 60
Where:
Room Volume is in cubic feet ($ft^3$).Target ACH is the desired number of air changes.60 converts hours to minutes.
Example Calculation
Imagine you are sizing a HEPA air purifier for a standard living room.
Room Dimensions: 15 ft (L) × 20 ft (W) × 8 ft (H)
Target ACH: 5 (Recommended for reducing airborne allergens)
Calculate Volume: $15 \times 20 \times 8 = 2,400 \text{ ft}^3$
Apply Formula: $(2,400 \times 5) / 60$
Result: $12,000 / 60 = 200 \text{ CFM}$
You would need a fan or air purifier rated for at least 200 CFM to effectively ventilate this space 5 times per hour.
function calculateVentilation() {
// 1. Get Input Values
var length = parseFloat(document.getElementById("roomLength").value);
var width = parseFloat(document.getElementById("roomWidth").value);
var height = parseFloat(document.getElementById("roomHeight").value);
var targetACH = parseFloat(document.getElementById("targetACH").value);
var resultsArea = document.getElementById("resultsArea");
// 2. Validation
if (isNaN(length) || isNaN(width) || isNaN(height) || isNaN(targetACH)) {
alert("Please enter valid numbers for all dimensions and the target ACH.");
return;
}
if (length <= 0 || width <= 0 || height <= 0 || targetACH <= 0) {
alert("Values must be greater than zero.");
return;
}
// 3. Calculation Logic
// Volume = L * W * H
var volume = length * width * height;
// Required CFM = (Volume * ACH) / 60 minutes
var requiredCFM = (volume * targetACH) / 60;
// Convert CFM to Liters per Second (L/s) for international reference
// 1 CFM ≈ 0.471947 L/s
var requiredLPS = requiredCFM * 0.471947;
// Calculate time for one air change in minutes
// Time = 60 / ACH
var turnoverTime = 60 / targetACH;
// 4. Update UI
document.getElementById("resVolume").innerHTML = volume.toLocaleString("en-US", {maximumFractionDigits: 1}) + " ft³";
document.getElementById("resCFM").innerHTML = requiredCFM.toLocaleString("en-US", {maximumFractionDigits: 0}) + " CFM";
document.getElementById("resLPS").innerHTML = requiredLPS.toLocaleString("en-US", {maximumFractionDigits: 1}) + " L/s";
document.getElementById("resTime").innerHTML = turnoverTime.toLocaleString("en-US", {maximumFractionDigits: 1}) + " minutes";
// Show results
resultsArea.style.display = "block";
}