Enter the heat dissipated inside the enclosure and the temperature rise you can accept, and get the forced-air cooling airflow in CFM and m³/h — corrected for altitude and inlet temperature. Works for control panels, PLC cabinets, server racks, UPS and inverter cabinets, battery cabinets, telecom shelters, kiosks, generator canopies and LED walls.
No signup · Works on mobile · Formulas shown below · Updated 2026-08-23
Heat Load → Cooling Airflow
Q = P ÷ (ρ · cp · ΔT). Add a margin for filters and the fan curve; this tool does it for you.
Results
Engineering estimate for preliminary sizing. Verify against the fan curve, local codes and your system measurements before purchase. Ask a Longwell engineer to check your duty point free of charge.
How the calculation works
Forced-air cooling removes heat by warming a mass flow of air. The airflow needed depends only on the heat to remove, how much warmer the air may get, and the air density (which drops with altitude and temperature):
Q [m³/s] = P [W] ÷ ( ρ [kg/m³] × cp [J/kg·K] × ΔT [K] ) // ρ ≈ 1.20 kg/m³ at sea level, 20 °C; cp ≈ 1006 J/kg·K Sea-level shortcut: m³/h ≈ 3.0 × P [W] ÷ ΔT [K] or CFM ≈ 3.16 × P [W] ÷ ΔT [°F] (the classic "CFM = W ÷ (1.08 × ΔT°F)" rule is the BTU form of the same equation)
This tool calculates density from the site altitude (ISA model) and the inlet temperature, then adds a margin for filter loading and the fact that fans deliver less than their free-air rating once there is any resistance. If the enclosure is sealed (IP54+) against dust or rain, forced ventilation is not an option — use a heat exchanger or cabinet air conditioner and size it on the same heat load.
Typical temperature rise and ambient limits
Equipment
Typical ΔT
Max outlet / internal
Notes
PLC, relays, small PSUs
8–10 K
55 °C
Heat load ≈ sum of component losses
Variable-speed drives, servo amplifiers
10–15 K
45–50 °C
Losses ≈ 3 % of drive kW
UPS and battery chargers
10 K
40 °C
Losses ≈ 5–8 % of rating
Servers / IT racks
10–15 K
35 °C inlet (ASHRAE A2)
Heat = 100 % of IT power
Li-ion battery cabinet (BESS)
5–8 K
35–40 °C cell
Keep cell-to-cell ΔT < 5 K
Solar / string inverter
15–20 K
50–60 °C
Losses ≈ 2–3 % of rated kW
EV charger power cabinet
15 K
55 °C
Losses ≈ 4–5 % of output
Transformers, dry type
15–20 K
per class (B/F/H)
Losses from nameplate
Generator enclosure
15–25 K
50 °C
Radiated heat ≈ 8–12 % of engine kW
LED display / lighting
10–15 K
50 °C
Heat ≈ 70–85 % of electrical input
Worked example: 1.5 kW drive cabinet
Given: 1,500 W of losses, 40 °C ambient, outlet allowed to reach 50 °C (ΔT = 10 K), sea level, filtered cabinet.
Select a fan that delivers ≥ 595 m³/h at ~50 Pa (filter) — e.g. two 172 mm EC axial fans or one 190 mm backward-curved EC fan with temperature-controlled 0–10 V speed.
Design tips that avoid call-backs
Push or pull? Pressurising the cabinet (fan at inlet, filter in front of fan) keeps dust out; exhausting (fan at top outlet) removes heat faster from the hottest zone. For filtered cabinets, blow in at the bottom and let air leave through a filtered louvre at the top.
Inlet/outlet area should be at least 1.5× the fan swept area, otherwise the fan works against its own grille.
Speed control. EC or PWM DC fans with a thermistor cut noise and fan wear by running at 30–50 % most of the year. Sizing at the worst case, then modulating, is cheaper than over-sizing.
Hot-spot check. Bulk ΔT says nothing about a heatsink jammed in a corner — keep a clear path from inlet to the hottest component.
Redundancy. For unattended cabinets (telecom, EV charging) use two fans each sized for ~60 % of the load, and monitor tacho signals. See the Fan Wall Redundancy Calculator.
Frequently Asked Questions
How many CFM do I need to cool an electrical enclosure?
CFM ≈ 3.16 × heat load (W) ÷ allowed temperature rise (°F), at sea level. For example 500 W with an 18 °F (10 °C) rise needs about 88 CFM, plus 25 % for a filter — about 110 CFM. In metric: m³/h ≈ 3 × W ÷ K.
How do I estimate the heat load of a cabinet?
Add the losses of every component, not their ratings: drives and power supplies lose 3–5 % of the power they pass, transformers and chargers 5–8 %, IT equipment converts 100 % of input into heat, contactors and PLCs a few watts each. Add solar gain for outdoor cabinets (roughly 400–800 W/m² of sun-facing surface on a dark enclosure).
Does altitude change the cooling airflow I need?
Yes. Air at 2,000 m is about 20 % less dense, so each cubic metre carries 20 % less heat. You need proportionally more volumetric airflow, and fans also produce less pressure at altitude. This calculator includes the density correction automatically.
Why does the fan catalog say 300 m³/h but my cabinet runs hot?
Catalog airflow is free-air, at zero static pressure. Filters, louvres and a crowded cabinet typically add 30–80 Pa, which can cut an axial fan's delivery by half. Select from the fan curve at the real static pressure, or use a backward-curved centrifugal fan that holds airflow against resistance.
Fan cooling or an enclosure air conditioner?
Use fans when ambient air is clean, at least 10 K below the maximum internal temperature, and the enclosure may be IP54 or lower. Use a heat exchanger when the enclosure must stay sealed but ambient is still cooler; use an air conditioner when ambient is hotter than the internal limit.
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