I put 2 servers in my closet which run at about 90F. The closet has a window, but simply opening the window doesn't drop the temperature very much even when it is 60F outside. If I open the closet door also, then the temperature matches the other rooms no problem: ~75F, but I'm worried I'm losing all the cool air inside my house and wasting A/C because of this.

I'd like to keep the closet door closed and rig something up to pump hot air out of the room just through the window. I'd like to do it as cheaply as possible and I don't care about how it looks.

I could install a window A/C unit, but that would cost $150. I was hoping I could buy a box fan for $10 and some ducting for another $10 to solve this problem. If I install the fan and the intake duct right next to each other, is that a problem? Do I need to seal the fan or intake duct to the window or is that just an optimization?

I'd really appreciate any advice! Thank you!


3 Answers 3


Question for you to ponder before spending any money: Do you live in the arctic? Almost certainly you do not, since you just said "you're worried about wasting AC air outside" if you open the closet door.

So with the postulation above, why do you think you can cool the closet with outside air? You cannot. I'd take the stance that there will be many days that the outside air is greater or equal to the 90 degrees you comment on.

Now in the winter time, how will you cool the closet?

The simple answer to your post if you are going to spend the money is to have a window fan, two way unit, or at least one "blower" unit setup, and then you ensure you run some 6" flex tubing from the outlet of the machines to the window, with the blower fan in the piping, anywhere.

Now this said, depending on the house you have, and the mod you are willing to do, you can vent the air from the server into the attic, or into the crawl space, but you still need a way for a cooler source of air to come back into the closet space. Without an equalized pressure differential, no amount of blowing is going to help you, unless you recirculate already hot air.

So..... Buy an AC? Open the window in the winter? It's generally best to not close off "appliances" that generate heat, in a closed space. Thus, you need to bring cool air in from somewhere, and where it comes from has to be controlled. The outside is not going to suffice for each day of the week and all seasons.

  • And that's before a discussion on humidity...
    – Tyson
    Commented Aug 19, 2017 at 15:40
  • @tyson: "Thus, you need to bring cool air in from somewhere, and where it comes from has to be controlled." (that is just ONE of the environmental variables I was lumping into that)
    – noybman
    Commented Aug 19, 2017 at 15:42

If I was trying to deal with this situation I would first vent the door to the closet. This could be done by cutting a hole in the door and placing a vent grate over it. Another alternative would be to replace the door with one that comes with a louvered panel.

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I would then install a decent quality room ventilation fan that mounts in the ceiling of the closet or on the wall. (Since you have a window there it is an outside wall and a wall vent fan would be easy to install). There is a wide range of fan types to choose from including typical bathroom fans. The ventilation fan that I am suggesting would vent out to the outside wall or through the roof.

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From your question it sounds like you are trying to find a quick and cheap way to ventilate this closet. But I will suggest that this is the wrong approach and you should approach this from a professional and craftsman like way. After all it sounds like you have placed some expensive equipment in this room and you should resort to protecting it in a proper way rather than some kludge.

Part of doing this properly will be to install a temperature controlled switch into the power line to the vent fan such that it shuts off when it is not needed. this can save considerable energy over the course of a year. This could even be implemented with some of the modern home automation gear with a WiFi controlled switch and an app that runs on the server and obtains the temperature from the sensors inside the server itself.

Any venting to the outside will want to be implemented with swinging vanes (especially for a direct wall outlet) to prevent outside weather from coming back in through the vent when the fan is not operating.

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  • This is good advice. - But OP has indicated that he's worried about losing all the cool air inside his house and wasting A/C because of this. He should modify your solution to ingest the makeup air from outside the house. Commented Aug 19, 2017 at 16:03
  • This elaborates w/some design on what I posted above (but adds significant cost & no value), it touches on the concerns I listed, however, it will not work for the application. I gave a dirty way to get somewhere with this-cheap, but the point I was driving home is that a CONTROLLED cooling system is the only correct way to solve the issue. You have equipment that generates heat, like an electric heater, likely 24/7! Its not the same thing as a 1-4 hour kitchen turkey baking, or a 20minute shower. No need for vents from the home to remove water vapor in his closet. He needs equalized pressure
    – noybman
    Commented Aug 19, 2017 at 16:17

The first thing you should ask yourself is whether or not the outside climate provides a feasible way to provide clean cool air.

  • If the air is humid or the window is unprotected from rain, do not attempt to use it.

  • If the air is polluted or contains dirt or pollen often, do not attempt to use it.

  • If the outside can get hot sometimes, then cooling using outside air is not a consistent option.

Based on the fact that you mention running air conditioning, the outside air is probably too hot to consider using consistently. If you weren't aware, A/C is basically a "heat pump", pulling heat out of your house. Buying a separate A/C would be redundant.

As another answer put it: "you need to bring cool air in from somewhere, and where it comes from has to be controlled. The outside is not going to suffice for each day of the week and all seasons."

Your best option is probably to create a system of ventilating between the closet and your main house. One option would be to leave the door open, or you could add a vent to your door or even replace the door with one that is made of vents.

You could also add an air duct that goes from the house A/C to the closet, to have the house A/C directly push cold air into the room. If so, you should also have at least one air exhaust vent to the rest of the house, so that the existing air has way to leave so that the cool air can enter without resistance.

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