The request we hear most often in server rooms is to set the air conditioner to 16-18 °C. The logic is understandable: the colder, the safer. However, this approach both wastes energy and often does not solve the real problem, namely hot spots.
In this article, we briefly explain what the server room temperature should be, where to measure it, and how to set alarm thresholds.
What is the recommended temperature range for a server room?
ASHRAE's thermal guidelines for data processing environments generally give the recommended temperature range for server inlet air as 18-27 °C. Within this range, equipment operates within the manufacturer's warranty and with a long life. The guidelines also define wider permitted ranges by equipment class; however, these should be considered for short-term deviations, not for continuous operation.
In the field, many facilities keep the inlet air at around 22-24 °C to buy time until the air conditioners kick in during a fault. Lower values generally provide no additional safety and only increase energy consumption.
Where should temperature be measured?
The right measurement point is the front of the cabinet where the server draws in air. The value shown on the air conditioner's display is often the return air temperature and does not reflect the real situation in front of the cabinets. A single thermometer hung on the wall is similarly misleading.
- Use at least one sensor on the cold aisle side of each cabinet row.
- In dense cabinets, place sensors at the bottom, middle and top levels; the top level is usually the hottest point.
- A sensor in the hot aisle is useful for verifying the air conditioner's return air value.
- Do not place sensors directly in front of the air conditioner supply outlet; they read lower than reality.
While the average room temperature appears to be 21 °C, a server on the upper shelves may be drawing in air above 30 °C. If there is a hot spot, the solution is often not lowering the air conditioner further but correcting the airflow.
Why does keeping the air conditioner at a lower temperature not help?
Setting the air conditioner lower than necessary does not eliminate hot spots, because the cause of hot spots is usually the mixing of cold and hot air. Empty slots in cabinets, open cable penetrations and cabinets facing the wrong direction cause cold air to mix with hot air before it reaches the server.
A low setpoint has another side effect: the air conditioner overcools the coil surface and removes unnecessary moisture, the room dries out and the unit uses extra energy for humidification. Also, as the setpoint rises, air conditioner efficiency generally increases; so even small increases within the recommended range show up on the energy bill.
Because server room air conditioners run every hour of the year, every degree of setpoint means a consumption difference that accumulates over the year. The exact savings rate varies with unit type, outdoor climate and room load; however, raising the setpoint gradually after the airflow has been corrected is, in many facilities, the first energy-saving step that requires no investment.
Steps for safely raising the setpoint
- First find the hot spots and correct the airflow: blanking panels, cable penetration seals, cabinet orientation.
- Record cabinet inlet temperatures for a few days and identify the hottest point.
- Raise the setpoint in one-degree steps, monitoring for at least a few days after each step.
- Stop before the hottest cabinet inlet approaches the upper limit of the recommended range, and update the alarm thresholds for the new situation.
The setpoint is adjusted from the unit's control panel, but the control logic (return air, supply air or a remote sensor) varies from unit to unit. For this reason, it is safer to make the change together with a technician who knows the unit.
What humidity values should be targeted?
In a server room, humidity is assessed together with dew point and relative humidity limits; relative humidity is generally recommended not to exceed 60%. A very dry environment creates static electricity, and a very humid one creates condensation risk. We explain in detail how humidity control is done and the causes of humidity alarms in our precision air conditioning humidity control article.
How should alarm thresholds be set?
Alarm thresholds should be set in two stages: a warning close to the upper limit of the recommended range and a critical level below the permitted limit. This way the team gains time to respond before the situation becomes critical.
What are the temperatures in front of your cabinets?
We measure temperature and airflow in your server room and give you written recommendations.
| Level | Cabinet inlet temperature (example) | Response |
|---|---|---|
| Normal | 18–27 °C | Routine monitoring |
| Warning | Above 27 °C | Same-day check of airflow and air conditioner status |
| Critical | Approaching the manufacturer limit (around 30-32 °C for most servers) | Immediate action, load reduction if necessary |
The values in the table are examples; exact thresholds should be set according to the manufacturer values of the equipment used and the facility's risk policy. The rate of temperature rise should also be monitored: a rise of several degrees within a few minutes is the earliest sign that an air conditioner has stopped.
How quickly does temperature rise when an air conditioner fails?
When all cooling stops, the temperature in a dense server room can rise by several degrees within minutes. The rate of rise depends on the room volume, the IT load and cabinet density. For this reason, in critical rooms a redundant installation is made instead of relying on a single air conditioner; you can find how to plan this in our N+1 redundancy article.
How do you verify your server room temperature?
For a short check, temperature loggers that record in front of the cabinets for several days can be used. These records show how the temperature changes during the day and on weekends, and where the hot spots are.
There are also checks that facility staff can safely do: seeing where the sensors are, spotting empty slots in cabinets and open cable penetrations, looking at the air conditioner filter indicator, and noting the alarm history. Any work involving the electrical panel, control board and refrigerant circuit, however, must be done by a qualified technician.
At YOİ Mühendislik, at the site survey we measure cabinet inlet temperatures, assess air conditioner capacity and airflow, and give written recommendations. For maintenance and faults of your existing units, our precision air conditioning service provides maintenance and fault service; scope and price are determined at the site survey.
Frequently asked questions
What temperature should I set the server room air conditioner to?
The goal is to keep the inlet air at the front of the cabinets within the recommended range of 18-27 °C; many facilities choose around 22-24 °C. The air conditioner setpoint should be adjusted by measurement to achieve this result.
Is 18 °C safer in the server room?
Generally no. A lower setpoint increases energy consumption and often does not solve hot spots, because the cause of hot spots is air mixing.
Where should the temperature sensor be placed?
Sensors should be on the cold aisle side, at the front of the cabinets, preferably at the bottom, middle and top levels. A sensor placed in front of the air conditioner supply outlet reads lower than reality.