LoadCairn / Cooling airflow guide
How to calculate data center airflow in CFM.
A first-pass airflow estimate starts with the sensible heat that air must carry and the temperature rise available across the stream. This guide explains the CFM formula behind LoadCairn's cooling-airflow calculator, shows the unit conversions, and makes the planning boundary explicit.
Core model
Sensible heat / planning only
CFM = sensible heat load (BTU/hr) ÷ (1.08 × temperature rise (°F))
m³/h = CFM × 1.699
The coefficient is a simplified dry-air value at standard conditions. The result is a screening estimate, not an engineered airflow design or equipment rating.
01 / The planning question
What the airflow estimate answers
CFM means cubic feet per minute. In a cooling-airflow check, it represents the volume of air that would need to pass through a cooling path to carry a stated sensible heat load while the air warms by a stated amount.
A smaller temperature rise requires more airflow for the same heat load. A larger temperature rise permits less airflow in this simplified relationship, although the chosen rise still needs to make sense for the room, equipment, containment strategy, and cooling system.
The calculator keeps the arithmetic visible in the browser. It does not infer a room layout or select a cooling unit, so the estimate is most useful early in planning and as a sanity check against a more detailed design.
02 / Formula
The CFM equation
The calculator normalizes heat and temperature inputs first, then applies the same Fahrenheit-based formula for every valid scenario.
CFM = sensible heat load (BTU/hr) ÷ (1.08 × ΔT (°F))
denominator = 1.08 × ΔT (°F)
The 1.08 factor has units of BTU/(hr·CFM·°F). Multiplying it by the temperature rise gives the sensible heat carried by each CFM per hour under the simplified model.
Use a positive temperature rise. A zero or negative rise cannot produce a valid result in the calculator.
03 / Unit normalization
Converting kW, °C, and m³/h
The visible calculator accepts common planning units, but it converts them to the same internal basis before calculating CFM.
Heat load
1 kW = 3,412.14 BTU/hr
Multiply kW by 3,412.14 to get BTU/hr.
Temperature rise
ΔT (°F) = ΔT (°C) × 1.8
The calculator applies a 1.8 factor to °C temperature rise.
Airflow output
m³/h = CFM × 1.699
The metric value is derived from the unrounded CFM result.
04 / Worked example
Example: 10,000 BTU/hr at a 20°F rise
This example mirrors the calculator's illustrative starting values. It demonstrates the arithmetic only; it is not a recommended data center design value.
- 1. Normalize the inputs.10,000 BTU/hr ÷ 3,412.14 = 2.93 kW
20°F ÷ 1.8 = 11.11°C - 2. Apply the CFM formula.CFM = 10,000 ÷ (1.08 × 20)
CFM = 10,000 ÷ 21.6 = 462.96, or about 463 CFM - 3. Derive metric airflow.m³/h = 462.96 × 1.699 = about 786.6 m³/h
If you enter approximately 2.93 kW and 11.11°C in the interactive calculator, its unit normalization follows the same relationships. Small differences in the displayed final number come from input rounding and the calculator's display precision.
05 / Inputs and assumptions
What to bring to the estimate
The calculator needs two values. Be explicit about what each value represents before comparing the result with a cooling unit or room plan.
- Sensible heat load
- Use the heat that must be carried by the air stream, entered in BTU/hr or converted from kW.
- Temperature rise
- Use the temperature difference across the cooling air stream, entered in °F or normalized from °C.
- Airflow result
- The result is an estimated volume flow in CFM, with an equivalent value in m³/h.
- The entered load is sensible heat only. Latent heat from moisture is excluded.
- The 1.08 BTU/(hr·CFM·°F) coefficient is a simplified dry-air sensible-heat factor at standard conditions.
- The estimate makes no correction for air state, humidity ratio, barometric pressure, or elevation.
- The temperature rise is treated as the usable rise across the cooling air stream and must be above zero.
06 / Boundaries
What this CFM number does not tell you
The estimate uses sensible heat only and a simplified dry-air coefficient at standard conditions. It makes no air-state or elevation correction.
- Latent cooling, dehumidification, or moisture added by ventilation and infiltration.
- Rack layout, containment leakage, bypass air, recirculation paths, and distribution losses.
- Fan heat, coil performance, filter pressure drop, static pressure, and equipment controls.
- Redundancy, diversity, operating modes, design weather, or a manufacturer’s rated airflow.
Treat the result as a planning estimate, not an engineered airflow design or an equipment rating. A detailed project review should account for the actual air path, equipment performance, operating modes, pressure, redundancy, and applicable standards.
07 / Review checklist
Before using the number
- Is the heat input sensible heat, rather than a total load that includes a separate latent component?
- Does the selected temperature rise match the intended supply and return measurement points?
- Are the input units clear, and were kW and °C normalized before using the Fahrenheit-based formula?
- Will a qualified engineer review the air distribution, equipment ratings, pressure, redundancy, and site conditions?
08 / Run an estimate
Put the airflow formula to work.
Enter sensible heat and temperature rise in the interactive calculator to see CFM, m³/h, the calculation trace, and the same assumptions alongside your result.