Server room air conditioning
By Airva Editorial Team · Checked against published UK guidance · Updated
A server room is the one space in a commercial building where air conditioning is not a comfort system. Nobody sits in it. Its job is to remove a continuous, predictable heat load without interruption, and the consequence of failure is not discomfort — it is downtime, and possibly hardware.
The most common mistake we see is a comfort cooling unit installed in a comms room because it was cheap and the room is small. It works, right up until August, or until the office system's schedule turns it off at seven o'clock on a Friday.
Why comfort cooling is the wrong tool
| Requirement | Comfort system | What a server room needs |
|---|---|---|
| Operating hours | Office hours, scheduled | 24/7/365, no setback, no schedule |
| Load profile | Varies with occupancy and sun | Constant, driven by IT equipment |
| Failure consequence | Discomfort | Downtime, thermal shutdown, hardware damage |
| Humidity | Incidental | Actively controlled — too low risks static, too high risks condensation |
| Redundancy | None | Usually N+1 |
| Monitoring | Rarely | Essential, with alerting |
The single most dangerous arrangement is a comms room sharing a zone or a schedule with the office system. When the office system goes into overnight setback or weekend shutdown, so does the cooling for a room full of equipment that never stops.
What the design has to get right
Continuous duty. Equipment specified for round-the-clock running, not a comfort unit asked to do it. Duty cycles and service intervals differ accordingly.
Redundancy. For anything the business genuinely depends on, N+1 — two units each capable of carrying the load, alternating so both stay exercised. One unit means one failure takes the room out. This is the largest single cost decision on the page and it is a business risk judgement, not a technical one.
Sensible sizing from the actual IT load. The heat output is essentially the electrical draw of the equipment, which you can read from the UPS or the distribution board rather than estimate. This is the rare room where the load can be measured instead of modelled. Add headroom for planned growth, but resist wild oversizing — an oversized unit short-cycles and controls humidity badly.
Airflow that matches the racks. Cold air to the front of the equipment, hot air away from the back. Blowing cold air into the middle of a room and hoping is how hot spots form at the top of racks even when the room's average temperature looks fine.
Humidity control. Too dry raises static discharge risk; too damp risks condensation on cold surfaces. Comfort systems dehumidify incidentally as a side effect of cooling, which is not the same as controlling humidity.
Monitoring and alerting. Temperature sensors at rack height, with an alert that reaches a person out of hours. A cooling failure at 02:00 on a Sunday that nobody hears about is a cooling failure that becomes an outage.
Drainage. Condensate in a room full of electronics needs a considered, fail-safe route — ideally with a leak detector. This is a small line on a quote and a large problem when it goes wrong.
Where these rooms actually fail
- The office schedule turned the cooling off. As above. The most common cause and the most preventable.
- A single unit failed with no backup. No redundancy, no alert, discovered by users.
- Blocked airflow. Boxes stacked against a unit, or racks reorganised without anyone reconsidering the airflow path.
- Fouled filters and coils. Comms rooms are dusty and rarely visited. Capacity falls quietly over months.
- Condensate overflow onto equipment below.
- Growth outran capacity. Kit added year after year, cooling never revisited.
Most of these are maintenance and monitoring failures rather than design failures, which is why a maintenance schedule matters more here than almost anywhere else in the building.
Small rooms are not exempt
A comms cupboard with a couple of switches and a small server still generates continuous heat in a space with no ventilation and no thermal mass. The load is small but so is the room, and temperatures climb quickly once the door is shut.
For small rooms the sensible specification is a modest dedicated unit on its own control and its own schedule — genuinely independent of the office system — with a temperature alert. It costs little and it removes the single most common failure mode.
The compliance duties still apply
A server room system is commercial plant like any other:
- F-gas leak checks. Responsibility sits with the party using the equipment, records kept five years [1]. Intervals follow refrigerant charge, starting at least every 12 months from 5 tonnes of CO₂ equivalent — 2.4kg for R-410A [1].
- TM44. The 12kW threshold is the combined effective rated output across the building under one person's control [2] — so a small server room unit that would never qualify alone still counts towards the building's total alongside the office system.
- Planning. There is no non-domestic permitted development class for air source heat pumps [3], so external plant will generally need an application. See planning and compliance.
Note that continuous running makes servicing more frequent than the statutory minimum — quarterly is common for plant that never stops, which is industry practice rather than law. Our TM44 and F-gas guide separates the two.
What it costs
Server room cooling is priced from the IT load, the redundancy decision and the room, not from floor area. The N+1 question roughly doubles the equipment cost and is the main variable — which makes it a conversation about what an hour of downtime costs the business rather than a technical preference.
A single dedicated unit for a small comms room sits in the range of a comparable commercial split installation; a redundant close-control arrangement for a room the business depends on is a different order of project. Our commercial cost guide covers what moves the number, including the recurring compliance lines.
Frequently asked questions
Can I use a normal air conditioning unit in a server room? For a very small comms cupboard, a dedicated comfort unit on its own independent schedule can be adequate. It must not share a schedule or zone with the office system, and it should be monitored.
What temperature should a server room be? That is set by your equipment manufacturers' specifications rather than by a general rule — check them. What matters as much as the target is stability and the absence of hot spots at rack height.
Do I need two units? If the business cannot tolerate the room being down, yes — N+1. The question is what downtime costs you, not what the equipment costs.
Why does humidity matter? Too low increases static discharge risk; too high risks condensation. Comfort systems dehumidify as a side effect rather than controlling humidity deliberately.
How often should it be serviced? More often than a comfort system, because it never stops. Quarterly is common for continuously running plant. Statutory F-gas and TM44 duties sit on top of that [1][2].
Our comms room shares the office system — is that a problem? Potentially a serious one. Check what the controls do overnight and at weekends. Independent control is the cheapest resilience you can buy.
Get it designed around the actual load
Tell us about the room — IT load, rack count, whether the business can tolerate downtime, and what cooling exists now — and we will match you with one vetted, commercially capable installer: start a business enquiry.