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Server Room Cooling Calculator — IT Heat Load
Calculate cooling capacity for server rooms and comms rooms from IT equipment heat output. Includes UPS losses, safety margins, and N+1 redundancy per ASHRAE guidelines.
Total power draw from all IT equipment
ASHRAE: 18-27°C recommended
Extra unit for fault tolerance
Typical online UPS: 94-97%
1.2 = 20% margin
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How We Calculate This
This calculator determines the cooling capacity needed for a server room or comms room based on the total heat output from IT equipment and ancillary systems.
Heat load calculation
- IT equipment: 1 kW electrical input = 1 kW heat output
- UPS losses: (1/efficiency − 1) × IT load — the input the UPS draws above its output
- Lighting: All energy becomes heat
- Safety margin: Typically 1.2× (20%)
Design parameters
The cooling system must remove the total heat load while maintaining 18-27°C per ASHRAE TC 9.9. The required cooling capacity (kW) equals the total heat load times the safety factor — it is a fixed energy balance and does not change with the supply-air temperature difference.
The supply-air ΔT only sets the airflow needed to carry that heat (Q = ṁ·Cp·ΔT): a higher ΔT means less airflow for the same kW. This tool estimates airflow from a roughly 14°C supply air temperature, giving about an 8°C return-to-supply ΔT at a 22°C room (within the typical 8-12°C close-control range). N+1 redundancy adds one spare unit so cooling continues during maintenance or a unit failure.
Frequently Asked Questions
The cooling capacity must equal the total heat output plus a safety margin. All electrical energy consumed by IT equipment becomes heat — a server drawing 1 kW produces 1 kW of heat. Add UPS losses (5-10%), lighting, and a 20% safety margin. A typical small server room with 5 kW IT load needs approximately 6-7 kW of cooling.
ASHRAE TC 9.9 recommends 18-27°C (A1 class servers), with a target of 22-24°C. The previous standard of 20-22°C is now considered unnecessarily cold, wasting energy. Relative humidity should be 20-80% (non-condensing). Hot aisle temperatures of 35°C+ are acceptable with proper containment.
N+1 means installing one extra cooling unit beyond what is needed (N). If you need 3 units to handle the heat load, install 4. This ensures cooling continues if one unit fails, preventing overheating and equipment damage. Critical data centres may use N+2 or 2N redundancy for higher reliability.
Standard split AC units are suitable for small comms rooms (under 10 kW heat load) where precise temperature control is not critical. Precision (close-control) AC units maintain tighter temperature and humidity control, have higher sensible heat ratios (no wasted latent cooling), and are designed for 24/7 operation. Use precision cooling for loads above 10 kW.
UPS efficiency is defined as output power ÷ input power, so the heat the UPS dissipates is input − output = IT load × (1/efficiency − 1). A UPS at 95% efficiency carrying a 10 kW IT load adds 10 × (1/0.95 − 1) ≈ 0.53 kW of heat (the rougher "5% of load" approximation gives 0.5 kW). Include this in the cooling total, and also allow for power-distribution losses (~2-3%). Online double-conversion UPS units are typically 94-97% efficient; line-interactive units are 97-99% efficient.
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Last updated: March 2026
Verified against UK standards · estimates only, confirm with your supplier.