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I've just moved into an apartment without an air conditioner in Sunnyvale, California. The weather is not too hot, but there are going to be some pretty warm days in the summer, especially since I'm on the second floor of two. The temperatures at night should be cool enough to manage quite well - if I can get enough cool air in here!

There's no house fan, and it being an apartment, there's not much I can do about that. So what's the best way to circulate air with standalone fans?

Added fun: a neighbor smokes near my main windows, so I'd really prefer to pull air in through a screen door instead.

(I'm from Texas originally, where no one would dream of building anything without air conditioning, so I have absolutely no experience with this!)

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    If you use the box fan to blow warm air out the smoking window, cool outside air should come in the non-smoking windows. – Tester101 Jun 20 '11 at 11:58
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Ideally, you would blow warm air out of your apartment. Cool outside air will naturally take its place. If you can take advantage of prevailing winds by having open windows on opposite sides of the apartment, do so. Otherwise, use a box fan blowing out of the screen door (assuming it's not in a bedroom -- they can be pretty noisy) and smaller fans pulling air in through other windows.

You can also keep the apartment cooler during the day by closing blinds. If you have a balcony that gets sun during the day, consider getting some large plants: they'll provide some shade, and they'll need watering, which will also help to bring temperatures down.

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  • The other current answer suggests pulling in the cool air. What reason is there to push warm air out instead? – Cascabel Jun 20 '11 at 13:27
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    @jefromi: to get air circulation through the whole apartment. – Niall C.♦ Jun 20 '11 at 14:15
  • By pushing air out, you create a "negative air pressure" space, where outside air will come in any way it can, including where you don't have fans drawing air in, but do have open windows or small leaks (EVERY house has a few air leaks). This generally cools the house faster. – KeithS Jun 20 '11 at 22:17
  • Okay, but if you pull warm air in, it creates a positive pressure, and pushes air out everywhere, whether or not there are fans there. What's the difference? – Cascabel Jun 21 '11 at 2:32
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    Okay, I'll answer my own question then: pushing and pulling should create roughly the same quantity of air and thermal flow, but the distribution is different. Pulling cool air in dumps all the cooling in one place, while pushing warm air out spreads the cooling across all available inlets. – Cascabel Jun 21 '11 at 13:39
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I moved to Sunnyvale from Chicago. What I found to be the most effective:

  • Two fans. One blowing on me, one in the window pulling in the cooler night air. (As for your smoking neighbor, politely asking them will most likely change their behavior (most smokers aren't a**holes) and if not, you'll find CA has very aggressive anti-smoking laws. In many cities smoking within 50' of a residential window is illegal.)

  • Close the blinds during the day.

  • Avoid apartments on the top floor of the building (if it's not too late)

  • Not really DIY tip, but applicable to your situation: Take a cool/lukewarm shower prior to bed. It cools your skin off & the continuing evaporation makes a big difference. (I learned this trick in China, where summertime AC isn't so popular.)

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Unfortunately, I think the fan idea is unlikely to work very well. When you exhaust the hot air in the apartment, that creates a negative pressure, which pulls air in from elsewhere. Where is that air going to come from? Outside. Where the air temperature is hot. See the problem?

I lived in a second-floor apartment in the south bay for several years. Even with a small wall-mounted AC unit, it was close to unbearable, because most of the construction around there involved uninsulated walls and roofs, and single-pane windows. As a result, despite the relatively mild climate, the buildings overheat from solar gain. A month in and you'll be practically dying, trust me.

You could buy multiple window AC units. They're not that expensive (to buy, running them is another matter...). Unless your apartment has no hallways, a single unit is unlikely to work well since it has no air distribution ability, so rooms far away from where it's located will still be hot. You'll probably need one unit for the living area and another for your bedroom.

Another option is a window swamp cooler. Swamp coolers are not as common in the bay area but can work very, very well. In the summer, the afternoon relative humidity in Sunnyvale drops to 30% at an 80 degree outside air temperature. At a pressure of 30 inches of mercury, we can calculate the wet-bulb temperature as 60.41 degrees. And a good 90% efficient swamp cooler will produce air very close to that. It'll be blowing air that's about 62 degrees.

Here is the formula for how much a swamp cooler can cool the air:

cooled air temp = outside air temp - ((outside air temp - wet bulb temp) * efficiency
of unit)

You'll only need one swamp cooler, since it blows the cold air through the apartment, with you directing the flow by opening faraway windows. So you could put in a window in your living area, open a window in your bedroom, and the cool air will blow through both the living room and the bedroom, cooling down both rooms.

Bonus: swamp coolers are dramatically cheaper to run than air conditioners. Mine uses 200 watts of power and cools my entire house to 73 degrees when it's 95 and sunny outside. My south bay apartment's pitiful AC unit used 1.5 kW of power and still couldn't get the job done, and my bedroom was always incredibly hot. I slept in the living room during much of the summer.

If I could go back in time and tell my former self what I know now, I would definitely have installed a window swamp cooler. It would have made an enormous difference compared to that terrible AC unit. The south bay area is definitely a climate that can support them.

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  • The whole premise here is that the air outside is often much cooler. Without AC, and even with open windows, my apartment is often still 80-90F by the time it's down to 60-70 outside. Blowing/pulling that air in is a pretty big deal, both for cooling off in the evenings and for pre-cooling in the mornings so it doesn't get as bad in the afternoon. – Cascabel Jun 25 '14 at 15:44
  • I welcome you to give it a try. Nighttime ventilation is a time-honored strategy. But if your apartment is reaching 80 or 90 inside, I don't think it's going to help much. In NM where I live now, it cools off to 55 at night, and that's only sufficient to "pre-cool" the house to about 77 from the prior day's interior high of 90. Without mechanical cooling, the interior temperature will rapidly rise throughout the day. I think you will probably still be experiencing 85+ interior temperatures for large parts of the day with your ventilation-only approach. – iLikeDirt Jun 25 '14 at 15:50
  • Well, you might notice that this question is two years old. I'm still in the same apartment, and the fan is sufficient for days getting up to 80-85F (the average high is 80F). I do have an AC for hotter days, but the fan definitely, definitely helps. – Cascabel Jun 25 '14 at 15:53
  • Oh ha, I did not notice that! – iLikeDirt Jun 25 '14 at 16:03

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