Difference between exhaust air and intake air temperature.
Please enter valid positive numbers for Heat Load and Temperature Rise.
Required Airflow Rates
Cubic Feet per Minute:0 CFM
Cubic Meters per Hour:0 m³/h
Liters per Second:0 L/s
*Calculation assumes standard air density at sea level (1.225 kg/m³).
function calculateAirflow() {
// 1. Get DOM elements
var heatInput = document.getElementById("heatLoad");
var heatUnit = document.getElementById("heatUnit");
var tempInput = document.getElementById("tempRise");
var tempUnit = document.getElementById("tempUnit");
var errorDiv = document.getElementById("errorMsg");
var resultDiv = document.getElementById("resultBox");
var cfmOut = document.getElementById("resCFM");
var cmhOut = document.getElementById("resCMH");
var lpsOut = document.getElementById("resLPS");
// 2. Parse values
var heatVal = parseFloat(heatInput.value);
var tempVal = parseFloat(tempInput.value);
// 3. Validate inputs
if (isNaN(heatVal) || isNaN(tempVal) || heatVal <= 0 || tempVal <= 0) {
errorDiv.style.display = "block";
resultDiv.style.display = "none";
return;
}
errorDiv.style.display = "none";
// 4. Normalize to Base Units (Watts and Fahrenheit)
// Formula constant 3.16 relies on Watts and Fahrenheit Delta T
var baseWatts = 0;
// Convert Heat to Watts
if (heatUnit.value === "watts") {
baseWatts = heatVal;
} else if (heatUnit.value === "kw") {
baseWatts = heatVal * 1000;
} else if (heatUnit.value === "btu") {
// 1 BTU/hr = 0.29307107 Watts
baseWatts = heatVal * 0.29307107;
}
var baseTempF = 0;
// Convert Temp Rise to Fahrenheit
// Note: Since this is a Delta T (Difference), the conversion is different than absolute temp.
// 1 deg C delta = 1.8 deg F delta.
if (tempUnit.value === "f") {
baseTempF = tempVal;
} else {
baseTempF = tempVal * 1.8;
}
// 5. Calculate CFM
// Standard Formula: CFM = (3.16 * Watts) / Delta_T_F
// The constant 3.16 is derived from: 3.412 (BTU conversion) / 1.08 (Sensible heat factor)
var cfm = (3.16 * baseWatts) / baseTempF;
// 6. Convert to other units
// 1 CFM = 1.69901 m3/h
var cmh = cfm * 1.69901;
// 1 CFM = 0.471947 L/s
var lps = cfm * 0.471947;
// 7. Display Results
cfmOut.innerHTML = cfm.toFixed(2) + " CFM";
cmhOut.innerHTML = cmh.toFixed(2) + " m³/h";
lpsOut.innerHTML = lps.toFixed(2) + " L/s";
resultDiv.style.display = "block";
}
How to Calculate Cooling Air Flow
Whether you are designing an electrical enclosure, a server room, or a custom PC build, managing heat dissipation is critical for component longevity. The goal of cooling airflow calculation is to determine exactly how much air must move through a system to remove a known amount of heat while keeping the temperature rise within acceptable limits.
The Airflow Formula
The fundamental equation used to calculate the required airflow for cooling relies on the relationship between heat load, air density, specific heat capacity, and temperature rise. For standard air at sea level conditions, the simplified formula is:
CFM = (3.16 × P) / ΔT
CFM: Cubic Feet per Minute (Airflow rate).
P: Total heat load in Watts.
3.16: A constant factor derived from the specific heat and density of air at sea level.
ΔT: The allowable temperature rise in degrees Fahrenheit (°F).
If you are working with metric units, the formula can be converted to determine Cubic Meters per Hour (m³/h) or Liters per Second (L/s), as shown in the calculator above.
Understanding the Variables
1. Heat Load (Dissipation)
This is the total amount of energy generated by the equipment inside the enclosure or room. It is typically measured in Watts or BTU/hr. For electronics, the power consumption (in Watts) is often used as a conservative estimate of the heat load, assuming 100% of the energy consumed is converted to heat.
2. Allowable Temperature Rise (ΔT)
This is the most critical design parameter. It represents the difference between the temperature of the air entering the system (intake/ambient) and the air exiting the system (exhaust).
Example: If your ambient air is 25°C and your equipment can safely operate in an environment up to 35°C, your allowable temperature rise (ΔT) is 10°C.
Why Air Density Matters
The standard formula assumes you are at sea level. Air becomes less dense at higher altitudes, meaning it has less mass per unit of volume. Since the mass of the air is what actually absorbs heat, you need a higher volume of air (more CFM) to achieve the same cooling effect at high altitudes. If you are designing for locations above 2,000 feet, consider adding a safety margin of 10-15% to your calculated airflow requirements.
How to Use This Calculator
Determine Heat Load: Add up the wattage of all components inside the enclosure.
Set Maximum Temp Rise: Decide how hot you can allow the air to get before it exits. A lower ΔT requires more powerful fans.
Calculate: Input these figures to see the required CFM.
Select Fans: Choose a fan that provides slightly more than the calculated CFM to account for backpressure and air filters.