Most air conditioning is designed around people: a hot afternoon, an office full of staff, a bedroom at night. A server room is a different animal. The equipment runs around the clock, it produces heat but almost no moisture, and it still needs cooling when it’s cold outside.
This guide covers what an engineer looks at: the heat load, year-round operation, backup, safe unit positions, alarms and the F-Gas rules.
Why a server room isn’t like an office
Three things set a server room apart. First, the load is continuous. There’s no evening when the heat stops. Second, the heat is almost all sensible heat, the kind that raises the temperature, with very little moisture to remove. Third, the room still needs cooling in winter, when an ordinary comfort system may be switched to heating or struggle to run in cooling mode at low outdoor temperatures.
Small comms rooms are often cooled well by good-quality split systems, provided the model suits year-round cooling and there’s a backup. Larger rooms are a different job: see our data centre and comms room page.
Sizing starts with the IT load
Nearly all the electrical power your IT equipment draws ends up as heat in the room. So the starting point for sizing is the real electrical load, not the floor area. UPS or PDU readings are the best source.
To that we add lighting, people, heat through walls and windows, and sun on an outside wall, plus sensible headroom for growth. At the site survey we ask for load readings and your plans for the next few years.
Redundancy: plan for the day a unit fails
If one unit is the only thing between your servers and an overheat, a single fault becomes an outage.
The common answer is N+1: enough capacity to carry the full load, plus one extra unit. In a small room that often means two units, each able to cool the room on its own. A controller runs them in duty and standby, swaps them over on a timer so they wear evenly, and brings the standby unit in automatically if the duty unit faults or the room gets too warm.
Running in winter
Cooling a room when it’s near zero outside is harder for some equipment than cooling it in summer. Each manufacturer publishes an outdoor operating range for cooling mode. We check it against the coldest conditions the outdoor unit will see, and keep the unit out of strong wind where we can. The controls should be locked to cooling, so nobody can switch the unit to heat from the remote.
Want it done properly? AirCon Doctor installs, repairs and services air conditioning and heat pumps across London and the South East, from our base in East Grinstead. We’re an F-Gas certified company and NICEIC approved. Get a fixed-price quote.
Where the indoor units go, and where the water goes
Never put an indoor unit directly above a rack. Indoor units make condensate, and a blocked drain or failed pump can drip water straight onto your equipment. We place units so their airflow reaches the equipment intakes without the unit sitting over anything electrical.
The condensate route needs the same care. A gravity drain to a proper outlet is best. Where a pump is needed, it should have an overflow safety switch that stops the unit, and ideally raises an alarm, before water escapes. Our guide to condensate pumps explains the options.
Monitoring and alarms
A failure at 2am on a Saturday matters most if nobody knows about it. A temperature sensor with alerts by email or text, or a connection to your building management system, gives you time to act. Many controllers also have an alarm output that can feed your existing monitoring.
Test the alarms at installation and at every service. If your room does overheat, our 24/7 emergency repair line is open around the clock.
Servicing and F-Gas leak checks
Units that run all year wear faster. Servicing at least once a year is the minimum; many server rooms are better on a six-monthly plan, which a maintenance contract keeps on track.
Leak checks are a legal duty for some systems. GOV.UK’s leak checking guidance sets the interval by the system’s refrigerant charge in tonnes of CO2 equivalent: at least every 12 months from 5 tCO2e, every 6 months from 50 tCO2e. Each system is assessed separately. For example, a split holding 1.2 kg of R32 (GWP 675) is about 0.8 tCO2e, below the threshold, while 3 kg of R410A (GWP 2088) is about 6.3 tCO2e and does need a yearly check.
What we check at the survey
- the measured IT load and the expected growth;
- where the outdoor units can go, and the pipe route to them;
- a safe condensate route that never passes over equipment;
- the power supply for each unit and whether it should be on protected supplies;
- how alarms will reach the right people.
Then you get a fixed-price quote. See our server room air conditioning page for more.
Quick answers
Can I use a normal split system in a server room?
Often, in a small room, provided the model can cool all year at low outdoor temperatures, the controls are locked to cooling and there’s a second unit as backup.
What size unit does a server room need?
It depends mainly on the electrical load of the equipment, because almost all of that power becomes heat. We add the other gains and some headroom for growth.
What does N+1 mean?
Enough cooling to carry the full load plus one spare unit, so the room stays cool if any single unit fails or is being serviced.
How often should server room air conditioning be serviced?
At least once a year, and often every six months because it runs continuously. Some systems also need a legal leak check, depending on their refrigerant charge.
Related services
- Server room air conditioning
- Data centre and comms room cooling
- Air conditioning maintenance contracts
- Emergency air conditioning repair
More advice
- Commercial Air Conditioning: What Businesses Need to Know
- Air Conditioning Condensate Pumps: When You Need One
- What Happens During an Air Conditioning Emergency Call-Out
- Air Conditioning Maintenance Contract: What It Includes and Is It Worth It?
- All advice
This guide is general information, checked against the sources linked on 30 October 2026. It isn’t legal, tax or financial advice. Rules, grants and product ranges change, so check the current position before you rely on it.