Outside-air Cooled PC

[Brian] came up with an interesting PC cooling setup. He lives up north where it’s chilly in the winter. Using a bit of dryer ductwork and he was able to harness the outside air to cool his box. The system uses a window insert along with a dryer hood to suck in the outside air with a PC fan. We hope the air is adequately warmed, as it is exhausted into the room. Join us after the break for more pictures of his setup.

Below are the duct fitting he used. This includes a hood for outside, a damper which closes with gravity, some scotch brite pad to act as a filter, a flexible duct, and a quick connect.

The next three images show the construction of the window insert. The filter and hood are on the outside of the board, and the quick connect on the inside. Although [Brian] shows a damper in his parts image, we’re not sure where that is actually installed. We think it would be best for this damper to have a servo actuator, as gravity won’t be enough to keep the wind from forcing it open.

120 thoughts on “Outside-air Cooled PC

    1. You must not live in a very cold winter climate. In places where the winter actually makes things really cold the air dries out a lot! Meaning the likelihood of any condensation is very minimal unless he has a humidifier. I could fill my metal water bottle up full of ice and very cold water and still not have it sweat in the winter.

  1. The damper is probably part of the hood – every hood I’ve installed had one integral to the design. You’re right, they aren’t sturdy enough to do any good, which is likely why it was left out of the end product.

    I doubt it appreciably warms the outside air — I spent a few months using my desktop in a 8’x8′ unheated space midwinter a few years back. The PC ran great – sustained overclocks that just weren’t stable for any period during the summer – but the space wasn’t warmed any measurable amount.

  2. I used to just open up the side of my tower and place in the window with the open side facing outside when in the middle of winter. It worked great for overclocking.

    You know what was best about my mod? I didn’t have to buy anything to be able to do it.

    Unfortunately, since the OP does not have a fan actively blowing the outside air into the PC case I don’t see this as being anything helpful, just a waste of money. There is not going to be all that much negative pressure to pull much cold air into the case since the case has lots of other venting holes that aren’t obstructed buy a long tube or scotch-brite.

  3. I had a similar idea. But my computing room/office is located on the front side of the house. Therefore, the wife would never allow me to have something that breaks aesthetic look of the house. (rolls eyes)

  4. Hmm, cold possibly humid air into a warm computer. Yeah, I can’t see anything wrong with that.

    I’m with evilspoons, slightest bit of humidity in the air results in a wet computer.

    Neat idea, I remember seeing the guy that cooled his computers with water from his pool years before. I just wish there was a little more to this, like an air to air heat exchanger instead of just raw outdoor air.

    1. have you lived in a winter climate, my feet are like sandpaper, i live by handcream in the winter, there is next to zero humidity in the winter, why you think people buy humidifiers

  5. “actually humidity tends to be lower in winter in cold places.”

    Current weather conditions where I am:
    43 deg F
    90% humidity

    yeah, not really condensation by law, but still that much humidity and things tend to get wet. I wouldn’t cool my PC with raw uncontrolled air.

    1. To bill:

      > “actually humidity tends to be lower in winter in cold places.”

      Current weather conditions where I am:
      43 deg F
      90% humidity <


      If you follow that link, it should show you the historic weather in my area for february 2014. Notice how we reached 0F a few times. I wish it showed the humidity as well.

      To everyone else. The solution your argument is to put a dehumidifier inline between the computer and the cold air source. Problem solved. you can all go home now.


  6. Actually bring in cold air even if it has a humidity rating of say 50% and heat it up to room temperature the humidity can drop drastically say to 2% as cold air holds much less moisture than warm air. I doubt condensation would be a problem in real cold weather. Warmer temperatures and the humidity could be a real issue imao.

    1. This would work very well. You could also do like one fellow did out there on the interwebs and put a vehicle radiator onto the water cooling system and have that stuck out the window as well, with a fan on it to focus the cold air onto the radiator itself. In my area that means you need to use a liquid that cannot freeze at temperatures of -50C or lower.


      That link shows the temperature without windchill for Watrous, Saskatchewan which is pretty close to where i live. It was actually colder that day in my immediate area due to being more out in the country with less wind breaks and such. Cities/towns are naturally warmer due to the many buildings and streets.

      Do the whole system right, and you could have a wickedly cold system.

      However, like i said in another reply, Just put a dehumidifier inline between your air source and the computers intake fan, and you will have solved a good 85-100% of the humidity issue. The air might get a little warmer, but if the dehumidifier has a cool air setting, it can cool down the air again and keep it’s humidity near zero. I.e Cold dry air.

      For the air source though, i recommend putting a steel enclosure around the air intake, so as to keep snow and other moisture as limited as possible. Done properly, and it should help lower the relative humidity as well, before it even reaches the dehumidifier.

      Another person, Fileark, mentioned a bit about how the temperature defines just how much actual moisture is in the air. It might be 100% humidity in -40C temperatures, but in +15C or so, that only comes out to being maybe 10% or higher for humidity. Anything below 50% humidity is supposed to be normal standards, so your computer should be able to handle that just fine, especially with a filter or two in place to catch the possible extra moisture and debree that Might be in the air.

      All in all, the advice on the web page is not bad advice per say, but rather it is incomplete.

  7. All it would take is a little open baggie of CaCl2 (average, run-of-the-mill road salt) to strip the air of its moisture. I’ve done this with my PC at school in northern NY for a while.

  8. @Bill and evilspoons

    Please read up before making ill informed statements

    The air will see an increase in temperature when going into the computer, hence a lowered relative humidity and no chance of condensation.

    The only time you will see condensation is when you take hot humid air and cool it down, and thats not happening here is it?

  9. condensation shouldn’t be a problem on the inside of the case, since the air is being warmed up, which increases the moisture it can contain, not decreases it. The only time it might be an issue is right when the computer is turned on, cooling the air in the computer, but I don’t see how that could have an appreciable affect. If its really cold out and humid inside I could see how condensation on the outside might become an issue, but you would notice it long before it caused any harm.

  10. Condensation won’t be a problem, warm air, cold surface = condesation. Cold air warm surface = no condensation.

    Else we’d all be fighting condensation with a normal cooled PC.

  11. Condensation happens when the water capacity of air is exceeded. Usually this happens when you cool down air, which lowers the water capacity.
    If you suck in cold air from the outside, it has about 95% humidity at most and warming it will LOWER that. So most certainly he will not have condensation happen in his PC.
    On the outside of the tube there might be condensation, though. Because of the outside air flowing through it, it will be way cooler than room temperature and get moist on the outside. But that’s about it.

    I solved my cooling problems by just hanging my home server relatively naked on the living room wall. Way better than any halfway normal case and the power usage slightly heats the room ;)

    1. this! ive had a few OC sessions putting the pc outside. i am thinking about doing it again right now and i googled to make sure and i kept on looking until here. he said it. i did it several times already with good results! works better on air cooled parts than on the liquid cooled btw. was trying to crack the 2200mhz at full load on my 3090FE^^ winterclocking is fun!

  12. @JFS et al.

    Not every surface in the computer case is activly heated. Fan grils, sides of the case, metal supports, screws, wires and cabling that the air flow comes in contact with first will cool down to the tempature of the incomming air. If the dew point increases outside, those surfaces will condense, and the water will drip down to other parts of the computer.

    Please think about the whole picture before making ill-formed statements.

  13. I am having a hard time understanding the economics/thermodynamics/need for doing something like this. If you bring in cold air to cool your PC, you will lose warm air somewhere else in the house unless you are pressurizing your house with the extra air. It takes energy/money to warm up that cold air. You can argue that the heat energy from the computer is waste heat that needs to be dissipated. But I would argue that the waste heat would be put to better use to warm the room/house. If you actually need the extra cooling, ie the computer will not work unless you cool it below room ambient temperature, that is a dodgy setup. What will you do during the summer months? Use an air conditioner to cool your computer?

    1. Thoughts here are…..in winter when the outside air is colder than the room temperature, draw in the colder air from outside and dissipate the heated air (from the computer) into the room). You’ll notice that by doing that, your room furnace won’t kick on as frequently. The cost benefit as I see it is that you will be running your computer more efficiently while also saving on your heating bill.
      In the summer when it’s hotter outside than the room temperature, just reverse engineer it so that the cold air comes from the room (assuming it’s air conditioned in the room or at least colder than the outside ambient temperature).

  14. Why not just go with a liquid cooled system with the radiator placed outside the window? The heater core out of a vehicle would be sturdy and just the right size. I think what he has done isn’t too bad, but I still believe there are better ways. It’s nice to actually see some simple hacks for once.

  15. @Bill Porter

    An increase in the dewpoint of the outside air coming into the case would have to result from either a change in the temperature or relative humidity. For what you are describing to be a problem the outside air would either have to have an RH of 100% or increase in temperature at a rate such that the new dew point temperature of the incoming air surpasses the temperature of the internal components previously cooled by the incoming air (which would also increase in temperature with the increase in temperature of the outside air, with a lag related to thermal time constant). Since temperatures outside tend to move rather slowly (a few degrees/h perhaps) I just can’t see that happening, though no one can really say definitively either way without making a detailed thermal model of the entire system.

    Either state your idea as a competing theory or do a proper analysis of the big picture before before accusing others of making ill-formed statements.

  16. It Should not need a fan to pull air into the case, if all other fans are exahsting, it will pull in what it needs. However, the heat loss from the un-insulated ducting and window adapter will add loads to the heat bill. Then if the wind is blowing you will have plenty of cold air blowing through the case into the room as well. I guess if your renting, and not paying for the heat, you don’t care.

    I don’t think condensation is a major issue because he is heating, not cooling the air. Cold air can not hold as much humidity (water vapor) as warm air If there is condensation it will likely be, mostly, on the outside of the case where the warm air strikes the cooler case surface. Now if you turn the fan off, and warm humid air migrates quickly into the case then there may be trouble.

    I like the idea to cool a computer using the cold air from outside, but I would opt to use insulated ducting, insulate the case, and exahst the air back to the outside if I were going to build something like this.

    My method is a bit simpler. I have a server closet and pull filtered air from the crawl space into the closet and force the hot air out through a roof vent. I can keep the closet closed and keep the heat load to a minimum year round. (Typlically even in the summer the crawl space temp is less than 70F

  17. @Bill

    So somehow you cool parts of the interior of the computer to below that of the outside air? Go read up on the second law of thermodynamics. I wasn’t trying to argue with you, I was responding to you shooting down an interesting approach to cooling a computer by making statements which hold no truth.

    Try to think of something constructive to say before you make your next post

  18. “. For what you are describing to be a problem the outside air would either have to have an RH of 100%”

    Um, that happens frequently when it rains, so it is a very real possibility.

    Also I don’t like to be negative, I was mocking JFS’s comment to me.

  19. Interesting idea. Guess if condensation was a problem, you could use a heat exchanger so there’s not any actual air flow from the outside to the inside. Maybe that would still have some condensation – been a while since I took thermo.

  20. @Bill Porter

    I don’t like to be negative either.

    I wasn’t thinking about rain at <32F temps, but supposedly (according to a quick internet search of unverifiable accuracy) the humidity can increase to 100% during snow – which I agree could cause problems if the air temperature is changing and you had components completely surrounded by the cool incoming air stream (such as a grill).

  21. I thought about doing this myself years ago but after considering the condensation risk i decided against it. Plus i was going to insulate the case and put the exhaust right back outside. But again condensation worried me too much.

  22. Just a few notes to the readers. I built this bc i was bored and thought on the idea really didn’t have a practical use for it. The window board actually fits perfectly in the window and doesn’t look crappy from outside, i still want to add some weather stripping to the top and bottom of the board for a better seal though. I actually finished the mod last night by dremeling out some of the case to increase airflow and mounted it to the case with zip ties, looks a lot cleaner and the new fan i put in can really move some air compared to the one that was in there.

  23. @Swighton

    Yeah, I wasn’t sure about snow either, but I live too close to the bible belt for comfort, so all I get is freezing rain (like today) which would scare the heck out of me to run outdoor air into my computer.

    I agree it’s unlikely in normal operation, but i wouldn’t bet my PC on it no matter where I live; but especially where I live now.


    “So somehow you cool parts of the interior of the computer to below that of the outside air? ”

    No, what I said was:

    “If the dew point increases outside”

    So maybe try to read your opponent’s comment carefully before you make your next post?

  24. There are simple ways to handle condensation, such as sealing the case well to prevent ambient interior air from entering at all. If you can maintain positive pressure with exterior air, I see no problems that would come up.

    When it’s below-freezing, the air from outside will likely be dry enough that it’s a non-issue, or the humidity will be cold enough that it won’t condense on the warmer computer parts.

    The real issue with condensation comes when a surface cooled by air from outside cause the interior air’s humidity to precipitate onto the surface. If you can avoid that, you’re golden.

  25. I did something a lot like this when i was in high School. i live in Canada where winters are wicked cold -20 to -35 C . i had a bathroom vent fan running outside in a box i made out of wood. i used a pair of my moms Pantyhose to stop the moist air and snow from getting sucked into the vent. then i ran the dryer vent in the window and cut a hole in my case. i was able to drop my temp from around 70 C to -3 C some nights even more if the outside temp dropped to -40C. i found out after a few days that i needed a vent going back out or you will be gaming in the cold . as long as you don’t get the cold air hit the warm air in the room you will be fine….

  26. In the spirit of this hack and living up in the colder states myself, I can see thee benefit of perhaps mounting the radiator of a water-cooling/heat-pipe solution outside. This would definitely alleviate the need for a fan on it in the winter and possibly in the summer also. If a heat-pipe solution were used, one could fashion an aesthetically pleasing cooling tower to be of benefit even in the heat of summer under full sun. Just my two-cents.

  27. So far i have not had any problems with condensation although i do unhook it if its going to rain of snow just incase. I really just threw this together because i was bored one night and decided to take a trip to home depot and see what i could make with a cheap budget. Didn’t really need it but it has cooled my rig about 3-5* although i havent really done any formal testing. I actually finished this last night by dremeling out some plastic on the side of the case for increased airflow and mounted the vent to the side of the case using zip ties so it looks alot cleaner.

    The board in the window actually fits perfect in the frame, i still want to add some weather stripping to the top and bottom of it for a better seal in the window but its fine for now. Sure it could use alot of tweaks but it was a fun little idea to build and helped kill some time.

  28. My server room (a small room off my office, designed so it could be plumbed as a bathroom if we ever sell the house) has to be cooled in winter as well as summer. In summer, a standard window AC unit keeps that and my office cool. In winter, I did something similar.

    I use the dryer hose intake similar to his (though mounted on a board that fits in the window frame) but it goes to a high CFM radon abatement fan that is inside a sound insulated box.

    I made the box out of wood and filled it with expanding foam (the fan stays cool because it flows fairly cold air — yes, I tested it). The OUTLET air on the box goes through a hole into a good sized automobile engine air intake filter (the old round kind) with a cap on it screwed back to the box.

    There’s also a charcoal filter around the outside. This keeps the dust, allergens, most odors, and a lot of the moisture from getting blown in.

    A simple thermometer controlled power switch from Grainger completes the setup. It works great.

  29. If some one wants to build a sub-zero liquid cooling setup for under $300, email me.

    I would like to see the overclocking ability with the setup that I have had knocking around my head for a few years….

  30. This is a really good idea. I did a ghetto version of this back in 1995, when I had a dodgy 166MHZ pentium based Win95 system that would BSoD hundreds of times per day (I now suspect that either the motherboard was toast, or the 166 MHZ Pentium was really a severely overclocked and re-labeled lesser chip.)

    In any event, I used cardboard tubing and a large ~120mm fan to make a forced air duct from my bedroom window (which overlooked a river so it was usually cooler than the surrounding area) to the side of the tower (opposite the cpu.) That instantly solved the problem.

  31. I actually did the same thing when I was going to school in Fargo, ND. It was impossible to keep a comfortable temperature in the room. Typically it was about 80 degrees F inside, when it was -20 degrees outside. Many people in the building simply left their windows cracked to stay try and stay comfortable(not very energy efficient). Also since the cold outside are was so dry, as well as the room air. I never had condensation on my computer despite the case being cold enough to freeze my beer.

  32. Unless that PC needs some serious subzero cooling because of overclocking, it would make more sense to better the heat exchange with the interior air of the house (with larger fans, more air circulation), and the PC would contribute to the heating effort for the house (hence helping to lower the heating bill).

    With this guy’s setup, what could happen is the PC case getting too cold, and starts to condensate the room’s ambient air on the exterior surface. With time, some could end up dripping inside, causing problems.

  33. Anyone degrading the viability of this mod due to condensation is at best pathetically misinformed.

    No, heating air will not cause condensation. Last I checked hair driers don’t spew water everywhere.

    All surfaces of the computer will be warmer than the outside air (which is likely to be drier than inside air either way). Your house won’t be humid enough to create condensation on the computer case unless you have mold growing everywhere already.

    If you want to bash this at least say moths are going to gunk up the heatsinks or something. TBH most computers are cheap enough to be disposable anyways.

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