A lot of people these days are building homes or buying homes that have network or A/V closets in them. On many of the higher end homes, these builders will hire audio-visual companies to actually do the installs and many times they will install a ductless mini-split air conditioner on the closet.  This will be to keep the amplifiers and other equipment more than cool enough to operate for extended periods of time.  That’s fantastic for those multi-million dollar homes.  But what about venting a server closet or A/V closet in a smaller home, or one that just has a few devices. Even small server and network closets at small businesses need to be vented. Equipment will just last longer and will not go into thermal throttle or thermal shutdown when it gets too warm, reducing performance or just outright shutting the equipment off.

Venting a server closet or A/V closet in your home or small business is really simple, and it is something builders should include when they build your home.  Even just a switch or two can bring an unventilated closet well over 110 degrees.  This is bad news for your home and the equipment!

Venting a Server Closet

Before we talk about venting a server closet the right way, I want to share with you my situation.  When we built the home, I originally had just a small router from Verizon FiOS in the room and a 24 port PoE switch for my cameras, and a really crappy D-Link NVR that I wouldn’t recommend to my enemies. In addition, this closet houses all of the cabling and switching for my home theater room. The server closet is about 4ft by 6ft, and it would stay about 90 degrees in this room at all times.  Something I felt was reasonable.

Over time, I upgraded the equipment in this room pretty significantly.  I added a wall-mount rack (see that project here), an additional 50 port PoE switch, two Core i7 1U Servers (see my project How to Build a 1U Server), a Synology NVR216 for recording my IP Cameras, a Synology Rackstation RS2416+ NAS/iSCSI, two rack-mount 1500KVA UPS, and finally a small pfSense firewall appliance (hands down the best firewall you can get, and its open source).

You may think that all of this is a lot of stuff that’s not really needed, and to some degree you are right, but just a single server, UPS, and switch are going to generate enough heat that the room should be vented. As you can imagine the heat generated in this room became so much that I had to start leaving the door open to keep the equipment from overheating. This compounded the problem. Computer equipment makes a lot of noise, and that noise was now diminishing the enjoyment of my theater room.  I needed a solution.

Venting Does not Mean Supplying

Before we go on, I want to clarify what I mean by venting.  We’re not interesting in supplying more air to the room.  The builder installed an A/C vent to this room during construction.  This is fine, but it will never solve the problem and could actually make things worse.

First of all, when the A/C is running you will make headway due to the cold air being injected into the room.  That makes sense, right?  The hot air will be pushed out under the gap at the bottom of the door, just like any other room.  However, when the A/C is not running heat is continuing to build and if its a mild day outside, the A/C may never run at all.  This means no venting will ever happen.  Bad news.

But it gets worse! In the winter months you will be injecting hot air into the room compounding the problem!  What we need to do is exhaust the warm air from the room, not inject air.

Adding a Server Closet Return

To solve for exhausting this heat, I took a two pronged approach.  The first is that I installed a return air vent in the server closet ducted to the return air side of the home A/C unit. That alone will make a huge difference, but it won’t solve the problem.  There will still be days that the A/C (or furnace) will never run. To solve for this I installed a continuous blower into the ducting for this room.  This fan will pull about 25 watts and continuously exhaust air from the room, even when the A/C or Furnace is idle.

Even though the fan is designed to be installed either at the return vent, or at the A/C unit by default, I opted to install the blower about three to four feet from the rooms return air vent inline with the ductwork.  I chose this location for one simple reason.  It reduces the noise of the fan to point where it is almost silent.  If you place the fan directly at the room return it will make considerable noise.

Additionally, I added a variable speed controller between the fan and the outlet to allow me to adjust the airflow of the fan should I ever want to slow it down, or simply turn it off.  I finished off the install by spraying insulating foam into all of the gaps and cracks round the new return vent.  I plugged the fan into the same outlet used for the furnace.  This means the maintenance switch will disable this fan in addition to the A/C and furnace when working on the system.

The Results of Venting my Server Closet

The results far exceeded my expectations!  Before adding this additional powered return my server closet would overheat and my equipment would start sending out warnings within half an hour.  Temperatures would rise to 110 degrees and eventually equipment would start turning itself off to prevent damage.

With the powered duct vent installed, the room maintains at about 80 to 85 degrees.  More than acceptable for my purposes! If you had more equipment you could step everything up to 8″, or with less you might be able to step down to 4″ versions of everything.

If you’d like to vent your server or A/V closet efficiently and not for much money I’ll provide links to everything I used below.

Items Used in this Project

10 Responses

  1. Franklin B.

    I don’t know why this isn’t the #1 site on the internet. This is something I have been hoping to figure out how to solve for a long time and could never find any decent information about how to accomplish it. My home theater closet is a sauna and I’ve been afraid my amplifiers were going to catch fire or die an early death. THANK YOU for this!

  2. Franklin Wolfgang

    This is how I vented my AV closet. It works perfect. I can tell you right now that you should be careful with these fans. They do eventually fail after many years of use and then your closet will overheat. The best way to handle this is to make sure you have a temperature probe on one your PCs and have it alert you if something fails.

    • Mike Murray
      Mike Murray

      Agreed! I have two monitors in the closet. One is Observium which monitors via SNMP. I also have ZWave probe from my home automation system in there.

    • Mike Murray
      Mike Murray

      All interior doors have a two inch gap between them and the floor for exactly this purpose. Standard home construction.

  3. Adam Joyner

    Makes sense. I’m going to be doing something similar with my mining closet. With my two 8 GPU mining rigs, things quickly became very toasty in there. Quick question. Since you have the exhaust pumping into the return side of the air handler, I’m guessing the hot air gets circulated back into the house when the A/C isn’t running? Possibly helps heat the house in the winter?

  4. mike

    Great Article! This is exactly the setup I was looking for. Forgive me for the very basic question, but what is the order of installation? I’m trying to find out how the fan is mounted and connected to everything. Also, would it be possible to just let it vent in to the attic and not connect to the return? I’m hesitant to cut into any of my existing hvac. Thanks again!

    • Mike Murray
      Mike Murray

      Not connecting it to your AC would cause a lot of issues and would be against code in most countries. You’d just be blowing all of your air conditioning into the attic like leaving your front door open 24/7.

      • Botts

        I run my duct with a splitter.

        In the winter, it goes into the cold air return line, and in the summer it goes outside.

        It’s just under the limit for needing make up air, but prevents me from having to cool the air through my A/C unit like I believe yours would.

      • Mike Murray
        Mike Murray

        I actually considered that, but there’s a an issue I didn’t like. When venting air to the outside you’re causing negative pressure in the home. For air to leave the house, new air must enter the home. This means it’s being pulled through cracks in your doors, etc. Pulling in outside pollens and the like. I didn’t want that.

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