I have a server room about 12 feet square with an unfinished ceiling (exposed ducts and wiring). It houses a few servers (about ten, 1U and 2U) and some networking gear (four 1U switches, three routers, three modems, two cable boxes).

With the door closed, it runs around 80 degrees Fahrenheit with half the servers turned on. When I turned on all the servers it reached 86 before I chickened out and propped the door open.

The room is adjacent to air-conditioned office space, but does not itself have dedicated air conditioning. The ventilation for this room seems to be limited to one duct coming in at ceiling level, with a powered fan to draw air in, and one duct at ceiling level to allow air to flow out (it seems like it may just go into the drop ceiling cavity in the adjacent room).

The adjacent office space stays fairly cool, but I'd prefer not to leave the door propped open all the time.

There is both 110v and 208v service in the room, and plenty of power available. But there are no windows, and no floor drains (in a pinch we might be able to run a condensation hose through a small hole we'd drill in the wall to a nearby sink area, but only if absolutely necessary).

I've considered portable A/C units, but I'm not sure on sizing and a lot less sure how we would run the exhaust hose(s). I suppose we could point one at the existing room exhaust duct (air return), but substantially modifying the duct is probably a no-no.

I've also considered installing a fan box in the door of the room, but I'm concerned that this will only drop the temperature a little. Even right now, with all the equipment on, the room is at 83 degrees with the door open. And the main building A/C turns off daily at 6 PM to conserve energy, so the adjacent room temperature rises at night.

How would you cool this room? Let's say the goal is to bring the temperature with everything running from a steady state of around 90 degrees down to 75 (equivalently, to offset the heat produced by ten 1U servers).

  • Couple questions: does "12 feet square" mean 12' on a side, or does it mean 12 square feet? ie about 3'x4' (I'd assume 12' on a side) And, when you say "one duct coming in a ceiling level," is that in the room next door? Oh, and how big is the room next door, and what's in it? May 7, 2010 at 2:44
  • Bizarre, when I try to edit my comment to take out the question about the duct (now that I see it's in the OP), I get two boxes, and an error message when I try to save an edited version. May 7, 2010 at 2:59
  • The room is like a cube, 12 feet on each edge. The adjacent rooms are much larger, and are office space with desks. May 7, 2010 at 11:22

8 Answers 8


I would use a portable air conditioning unit that consumed it's own condensation and kept the room at 50% relative humidity. Some people argue that dew point is a better metric, but I haven't looked into it deeply enough and am willing to be corrected. Some A/C units will push their condensation through a hose that snakes through the A/C unit's exhaust hose and thus gets evaporated into the hot, dry output air and into the plenum and exhaust system. You could also get an A/C unit that has condensation tanks and just remember to empty them every day. Annoying, yes. But sometimes an admins gotta do what an admins gotta do.

Either way, you must have exhaust. You can run a duct hose from the A/C's output into the plenum space or near the outtake. That might not be sufficient though. IMO, A/C output is your biggest problem here. Might be nice in winter, you can barter with different departments on which cubicle space the exhaust hose will run to each week. :)

Plenty of companies make portable cooling units made for permanent usage in server rooms. Some companies include:

  • Atlas
  • Topaz
  • Movin Cool (I think Atlas bought Movin' Cool, or the other way around, or something else. There seems to be some relationship between the two companies that I haven't determined yet)

I blogged about portable A/C units a little while back on my old blog here: http://thenonapeptide.blogspot.com/2009/12/list-of-portable-cooling-units.html

  • +1 for portable air conditioners, although you should consider pitching a more official server room imo. We used a portable airconditioner in our little wana-be server room at the time, luckily it had a window for AC exaust. 10,000 BTU's was plenty for 5 production (2-6U) Servers. Most units have a small hose and plug somewhere to drain the collected condensation, its important to check this during hot months because if it overflows the radiator/condenser within the unit will start collecting ice, which will ofcourse drastically increase humidity and cause possible leaking.
    – iainlbc
    May 7, 2010 at 3:15
  • This is the official server room. There's no possibility of moving it. Most of our stuff is elsewhere, but we need a few things within the office area, which this is. May 7, 2010 at 11:38

You really don't want to be stuffing about with this sort of thing or relying on guesswork. Just for starters I suggest you get that ceiling finished off and fitted with an exhaust fan or two.

For scaling the A/C I suggest talking to the A/C people, who know a lot more about this stuff than we do. Tell them the load you're currently running, after adding a bit more than than the maximum you can reasonably expect it to ever be. Don't forget to mention that it needs be be running 24/7. I actually prefer to have multiple units, each of which can handle the normal load, even if it's straining to do so. That way you can more easily deal with a failed unit.

In simple terms, the electricity your gear consumes exits as heat. Work out, or measure if you have the gear, how much you're using. If in doubt get an electrician to measure it for you. It's a small investment that can save you a lot of money later.

  • The ceiling cannot be finished, because among other things there is a 477v transformer hanging from it (putting a drop ceiling in would be difficult because the bottom of the transformer is as low as the ladder racks on the other side of the room). The 10 servers I mentioned use about 350 watts each typically. May 7, 2010 at 11:24
  • 1
    A very generic rule of thum, 1 ton of cooling per 750 VAC of UPS (keep your cooling in line with your power capabilities). (1 ton of cooling is approximatly 2500 BTU if you're using portable units). If you plan to add much more in the future, definitely call a consulting place in to size the AC system.
    – Chris S
    May 7, 2010 at 13:36
  • @John Zwinck, if the ceiling cannot be finished it's going to be harder to scale the A/C because the airflow is a much bigger variable. This makes it even more important to get some expert advice - or be very generous in your A/C rating. May 7, 2010 at 19:53

I've used one of the portable units in the past, and during peak temperatures, we were able to keep things about 20 degrees cooler. We'd also put some insulation on top of the drop ceilings, which seemed to help quite a bit. On a side note, you're lucky for the lack of windows - this "server room" had an entire wall of windows, which we went to great lengths to block off, as it was a huge source of additional heat.


Our server room is about twice as big and has about twice as many servers. Our A/C unit (also humidifier) dies - which is getting to be fairly frequent as it's 20 years old - we open the door between the server room and our adjacent workroom and either put a big fan in the doorway to blow cooler air in or put a portable A/C unit in the room with its exhaust in the adjacent room.

Neither of those are good long-term solutions, they make me think of this classic article about flawed quick fixes. The best solution would be to hook the server room up to the building's cold air supply, but you commented that you didn't think duct work was possible.

Other than that, Wesley beat me to suggesting a portable unit, that's probably your only solution, as long as you can duct the exhaust properly.


Interesting points to consider:

(I'm not sure why, but I seem to be the counterpoint to chris S on many things. Nothing personal Chris, it's just that my experience seems to run counter to yours. I'm a fellow old guy, but man, we must come from opposite universes.)

  • A 750VAC UPS, even if fully loaded with an army of toasters, does NOT require a ton of cooling. Even at the most aggressive cooling you might need 2800BTU to dump the heating load. Now, if you're running your data center in a solar collector, YMMV, but most folks don't do that. Wanna spend money on the assumption that you'll go back to circa 1999 data centers? Do you secretly hope that your firm will need to become a protein-folding rendering farm and Viennese Pastry Bakery? Go ahead and sink a fortune into cooling.

  • People running old school data centers (I have several that date back to the 1980's) often discover that (after the expensive 5 ton cooling system fails) they can actually cool their data center with a couple of ~5000W wall mounted a/c units and pay substantially less for A/C because EER ratings have grown quite a bit. Even switching to 100vac from 208.

  • You're better off to have two a/c units than one in most cases if you really care about reliability. The life span of consumer equipment is often 70% or more of that of commercial equipment. I'm a big BIG fan of split wall mounts, but if you have outside access, those wallmounts do a fair job - especially if they have economy cool options.

  • You might take into account the power of in-house cooling/ventilation. In many cases, having adequate ventilation dramatically lowers your cost of cooling. A big storage room with a rack of gear is better than a small room, because convection will dump your heat load. However, assisting with building A/C or circulating air is a good idea, if possible. Even fans can make a huge difference.

  • You don't have to run at -34F. In fact, most equipment does just fine @68 to 74F. There are reasons to run an ice cream shop/data center, but 90% of commercial users don't need it. In fact, as long as you stay below ~79F, you'll probably be in good shape. This is adequate for your typical 5-10 box windows clusterz that most small-medium businesses run. If you have an army of undead MCSEs and your volume licensing costs approach parity with the IT directors salary, you might as well waste money on providing overkill HVAC.

The single exception: If your electrical wiring and panel aren't really cut out for your needs (as in you might need to arc weld or run an exchange server, for instance), keeping the A/C below 85F is a good idea - breakers typically pop based on thermal expansion, and a hot breaker box will trip when it gets warm.

I'm ok with 74F but I wouldn't get much above 80F in a data center - poorly built electronic equipment (and that's basically everything built by every manufacturer in the last two decades) may fail or become flaky above 80 degrees. The old idea of keeping everything at -60F was based on even crappier equipment - things built back when tubes and selenium components were common. This equipment would eat itself if it got a little hot. Nowadays, it just stops working correctly.

  • Thank you for this. I found the image of undead MCSEs hilarious. We ended up installing louvers in the door to the hot room, which did virtually nothing (which is about what I expected). Since then, we just leave the door open to let the heat migrate into the (much larger) rest of the space. This probably makes the servers get dustier than they should, but it's simple and more or less works. Feb 16, 2011 at 5:10

At the risk of offending anyone, I think the idea of installing aircon in this scenario is crazy if you care anything at all about electricity prices. An aircon system is going to be expensive and frankly, why? I run the equivalent number of boxes that you've described in an active (fan blown) sealed 24U cabinet, with two ducts that go to the outside - like this one here http://www.acoustiproducts.com/en/ucoustic_active.asp At most the cabinet draws about 300W, a ratio of 1:10 of what you'll be drawing with 2 domestic aircons.

That's all it needs, and if you've got cool air coming in from your office, then you're going to be good to go. I have one of these units in my office, with two hoses going through holes cut in the window, and I work at a desk two feet from it with no discomfort or noise issues (office space is at a premium here in central Oxford, UK). The best thing of all is that it is about the greenest, cheapest solution. The only problem is that you need to drill to attach the hoses to your out-duct somehow, but let's face it you are going to be doing something along these lines regardless, especially if you are installing aircon.


Youo are going to need 2 AC units. I don't think you'll find something permanent or semipermanent to be cost effective so you are looking at a portable solution. I don't think you should count on using the intake from building air as a vent if they turn it off at 6pm. I'd consider venting it out the door, if you can't cut a hole into an adjacent space. Also remember you are not trying to cool the room, just the intake air on the servers/equiptment, meaning that it's ok for the room temp to be 90s so long as the intake air is in the 70s.


Also try to get an AC unit that is network connectable for things like alerting. If it's a unit that consumes it's own condensation in a tank, then the tank may get full.

Failing that--or perhaps in addition to, for redundancy--get a environment monitor to monitor heat and humidity (ACs can break).

Sending out an e-mail should be sufficient, but SNMP functionality may also be useful if you want to link in a monitoring system (that also checks your servers, etc.).

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