Strategies for Cooling IT Equipment Closets and other Small Spaces

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Most any company has a number of closets, branch offices and other locations that house some IT equipment, be it servers, VoIP gear, switches or UPSs. Some of these locations were planned to house IT equipment but in other cases it just sort of happened over time. As a result, many of these locations weren’t designed with the kind of cooling system that IT equipment requires – a situation that could shorten equipment life.

When it comes to small spaces such as branch offices or closets, you’ve got five ways to address the issue:

  1. Conduction: Heat flows through the walls of the space
  2. Passive ventilation: Heat flows into cooler air via a vent or grille, without an air moving device
  3. Fan-assisted ventilation: Heat flows into cooler air via a vent or grille that has an air moving device
  4. Comfort cooling: Heat can be removed by a building’s comfort cooling system
  5. Dedicated cooling: Heat can be removed by a dedicated air conditioner

The five methods differ in performance, limitations and cost. Let’s look at some of the issues to give you an idea what might work best in your situation.


If a closet is effectively sealed, as many utility closets are, then the only way for the heat to leave is by conduction through the walls. For this to work, the air in the closet must be hotter than the temperature on the other side of the closet walls. Practically, this means that the closet will always be hotter than the other ambient air within the building, and it will increase as the power level of the IT equipment increases. There are lots of variables to deal with here, including the size of the room (bigger rooms will accommodate more heat) and the materials used to build it (concrete will retain more heat than drywall, for example).

Passive and fan-assisted ventilation

Ventilation is a very practical method for closet cooling. For power levels below 700 watts, passive ventilation is effective for critical closets, while for levels of between 700 watts and 2000 watts, fan-assisted ventilation is appropriate. You can support even higher levels if you use higher capacity or multiple fan assist units. Likewise, for non-critical closets, passive ventilation is effective for up to 1750 watts, and fan-assisted ventilation is effective from 1750 watts to 4500 watts. Application considerations such as the placement of the air intake vent and fan-assist unit relative to the IT equipment can also increase cooling performance. And, as with the conduction method, the size of the room and building materials do come into play.

Comfort cooling

Using the same air conditioning system that cools the rest of the building to cool an IT equipment closet isn’t a good idea. If you simply add a duct and return for the closet, you’ll get big temperature swings as the building air conditioning cycles on and off. The alternative is to dedicate a zone to the closet, with its own thermostat. While this will keep the closet cool, you’ll be wasting lots of energy by having the air conditioning come on during off-hours just to cool the closet. In short, you’re forced to choose between wasting electricity on nights and weekends and living with large temperature swings in the wiring closet, which can shorten the life of your IT equipment.

Dedicated cooling

The most effective way to control closet temperatures is to install dedicated closet air conditioning equipment, but this is far more expensive and complex than using passive or fan-assisted ventilation. In general, when the power level in a closet exceeds approximately 2000 W for critical closets or 4500 W for non-critical closets, dedicated air conditioning equipment is recommended. Be sure to make accurate determinations of power draw, keeping in mind that actual power draw of specific equipment is well below the power rating on the back panel. For example, configurable routers with back panel nameplate power ratings of 5-6 kW typically draw only 1-2 kW in common configurations.

In some cases, though, you’ve got little choice but to use dedicated cooling, such as when the air outside the closet is dusty or subject to big temperature swings, or when restrictions on your lease make it impossible to add ventilation ducts. If that’s the case, see the APC by Schneider Electric white paper, “The Different Types of Air Conditioning Equipment for IT Environments,” for guidance on which system makes sense.

To learn more about the various systems described above, check out the APC by Schneider Electric white paper, “Cooling Strategies for IT Wiring Closets and Small Rooms.”