Our Server room is located in the middle of our building and has no access to a window or outside ventilation. I had a quote done by a local heating/air conditioning company to install a room specific temperature control module, but this was going to be quite an expensive addition.

We are a relatively small company (roughly 60 users) and our server room consists of 2 servers, 5 switches, 1 firewall, 2 Modems and a few UPS's. During the nights and weekends, the rooms temperature often peaks between 85-89 degrees and I've finally received some management support to do something about it.

The best (most cost effective) solution I've been able to find is to buy a portable A/C unit (8000-12000 BTU) and vent the unit (via the exhaust hose) into the drop ceiling plenum area. Our Server room is very small (roughly 8x5) and I am assuming the A/C unit will not need to work very hard to keep the room at a constant temperature.

My concern is with regards to venting the unit into the open drop ceiling (the plenum runs the entire area of the office). Will venting from the small server room into this area have a significant heating effect on the rest of the office? Also, does the A/C exhaust contain any moisture that will cause mold in the long term?

Let me know if you've had a similar issue and/or what solutions might be plausible.

  • Exhaust moisture will depend on the unit; check with the manufacturer. Check how your current HVAC system works, it's probably using the plenum as a return already, so it'll have good circulation. Try not to oversize the unit (or get one with an adjustable bypass); wear and tear is primarily due to start/stop cycles, not the run time. Lots of places use a similar setup. Small split systems shouldn't cost most than a couple grand.
    – Chris S
    Aug 31, 2010 at 15:06

3 Answers 3


We have done the exact setup, with far more equipment. You are actually spreading the heat to the entire office, but you are also getting help from the building HVAC to deal with the heat. Mold shouldn't be a problem if there is good air flow in the plenum. Most portable units have a condensation reservoir that will need to be checked and emptied.


I would recommend doing it right the first time. Do not hack together a cheap portable unit to cool your production equipment. In small server rooms I usually recommend going with a Mitsubishi Mr. Slim AC only unit. They offer very energy efficient units. The last project I did was a small server room with a three cabinet Toshiba phone system, three Dell 2U servers, two gigabyte switches, router, and a bunch of other misc equipment. I estimated the BTU output just over 5000. We installed a Mr. Slim 9000 BTU unit. Works very well. The room is at a constant 74-75F. I don't know the exact humidity however, but its probably around 50%.

You can get BTU estimates from your equipment manufactures website. Dell and HP had great information that was easy to find!


I use those portable A/C units for temporary cooling when moving equipment or in case of multiple cooling failures.

They work fine for the most part, but you will need to have plumbing installed for the condensation drain. Otherwise it will require a daily emptying of the collection bucket (which may be a problem over weekends when it is running the most).

I would price out a small dedicated A/C unit for the room with an outside condenser, as it may be a better long term solution.

As for sizing. Use your UPS to determine the total wattage of the equipment and then convert to BTU using 1 kW = 3412 BTU. Don't forget to add some extra load for lights, people and other miscellaneous equipment.


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