This instructable documents my quest for extremely superior air cooling for my desktop using found materials and the testicle-shrinking chill of a brisk Wisconsin winter. I achieved this by cutting two holes, one in the side of my case, and another in a board which I inserted into my window frame and attached with some wicked plastic ducting. Please read on for details!

Step 1: Hole / Fan Installation in Case

I am basically skipping this step since I did this a long time ago and didn't take any pictures or keep a diary of the event but if you want help there are many guides online already, a good one that I found just by googling is right here. The picture below is the ideal configuration of the hole however this is the top of the case and we want ours on the side for the purposes of this guide. (The second pic is my actual setup)

What you need is a hole in the side of your case, that is going to suck in cool air and blow it onto your preferred components. I chose to make my fan blow directly onto my CPU since I bought a big ol' heat sink with fan already. Specifically I purchased the Thermalright XP-90 shown here and below.

Some tips for this step are:
1. Be EXTRA careful to try and line up the hole you are cutting EXACTLY over your CPU, I used a laser level dohicky for this.
2. Also know your materials and what it takes to cut it, not all cases are made the same, some of the new aluminum models would probably be cut fine with a dremel but I had a tough steel case which I went overboard with and cut with a plasma cutter basically just because I had access to one.
3. Depending on your fan size and case you might have to improvise with the hardware, I thought I could get some screws to mount the fan on the case at a local PC shop but I ended up just going to a hardware store and getting some long screws, rubber washers (reduce vibration noise!), and nuts.

Step 2: Find an Ideal Barrier & Window

This was kind of done for me as my room in my new apartment has one window about 3' wide and the other about 5' wide so it was a no brainer to go with the smaller side window. Then you should find a barrier (ie. a piece of wood) that you can cut a hole in and that will fit inside your window frame semi-snuggly. I happened to find an old, busted computer desk that someone threw out next to my dumpster that I brought inside and left in my kitchen for a month or so, and when I went looking for a barrier for this project actually turned out damn near perfect with almost no modification. I wouldn't expect to be so lucky but just head to the hardware store if you can't find anything suitable.

As you can see this board fits pretty well with a little space on either side, THIS MIGHT BE NECESSARY OR YOU WON'T BE ABLE TO GET IT INTO THE FRAME OF THE WINDOW!

I just measured my hole and traced it (my 120mm fan is actually almost exactly the size of an audio cd) and then drilled a 1/2" hole (wide enough for jigsaw blade) on the perimeter of the larger traced hole and then used a jigsaw to cut out the rest of the hole, you could also just go buy a hole saw bit the size of your fan which might be cheaper depending on the fan size and material. You can see my super modern workshop below (it came with the apartment!) with all the latest trimmings of milk crate sawhorses and an amazing dropcloth waste removal system.

TIPS:
Make sure you cut the hole in the board thinking about where the computer will sit on the sill so there is enough room on either side for the CD drive to come out and to access the cables in the back if you need to.
It might be a good idea to sand the edges of the hole

Step 3: Prepare Your Duct!

This one will probably require some hunting and improvisation. Unless you want to order/buy a professional duct length you will need to find some container that you can make into a tube to direct airflow straight into your computer and not into your toasty room. This website helped my with some inspiration for materials, it has a table with common containers & sizes right here.

I ended up using a section of the tub my favorite fiber supplement comes in although as I mentioned a 120mm fan is about the size of a cd so a cd stack tube would work as well and I actually tried it first but it is a very hard plastic which was too difficult for me to work with.

I had a hard time deciding how to seal the duct onto my case and ended up cutting some cardboard tabs and screwing them onto the case (with the screws already holding the fan) and then just scotch taping them onto the duct plastic. Tape isn't the best but since I used the Caulk Cord to insulate it I think the seal is fine.
This caulk cord is really great and I just realized I could use it not only for this project but for sealing around all the fans inside my case for better control of the air flow. It is removable incase I want to modify this later.

TIPS:
try to get a pretty even cut so there are as few gaps as possible around the edge.
Something I didn't use but I might if it proves a problem later is some foam around the edge that sits against the barrier. This would be great as the computer will be really close to the window and it will be hard to get in there and attach the caulk to seal it against the barrier. (I am not even going to bother until I figure out how much air is really escaping into the room)

Step 4: Final Placement

Stick that sucker on the window sill and let the cool air in!

As you can see I caulked all around the board so hopefully the only cool air will be going into my computer. Be sure to move your hand slowly around the entire window and caulk any place you feel air coming through. Also remember that gap between the halfway open window that you have now, and be sure to stuff somethign in there, my final picture is the lovely, chic placement of some sweatpants in said gap.

This is my first instructable and could have been way better if I had taken more thought about it while doing the project but feel free to offer suggestions and improvements. I am thinking about possibly cutting another hole with some ducting going into the front air intake fan on the case as well as adding another fan to the other side of the wood barrier to really suck that air in.

I am running an AMD64 3200+ (non-OC) and right now my CPU temp is hovering around 29 C with an outdoor temp of 50F, I did this last year in a much worse but essentially the same setup and saw it drop as low as 15 degrees celsius (!) (of course I was freezing my ass off while using it because I didn't have the sweet duct!)

As a final motto: Be careful, have fun, and stuff your caulk in as many gaps as possible!