Keep Your Room Cool At Night By Facing Your Fan Out, Not In

Keep Your Room Cool At Night By Facing Your Fan Out, Not In

Running air conditioning can be very expensive, but you still need to cool down at night so you can sleep comfortably. Real Simple notes that a fan blowing air out of your room is better than one blowing in.

Photo by fauxto_digit

When your fan is facing out of the window, it blows hot air out of the room, which his replaced by cold air from outside. As the cold air comes in, the temperature will drop. It’s best if you have another window to open elsewhere so you can get a cross draft going too.

Keep in mind this only works at times when the outside air is actually cooler than the air inside — if that’s not the case, you’ll want the fan blowing directly at you.

A Cool Trick to Beat the Heat [Real Simple via Apartment Therapy]


  • Why would this work ?

    If you blow air into your room, pressure will rise and the excess air will need to go somewhere, maybe into the next room.

    If you blow air out, the pressure will drop and air from somewhere else (e.g. the other room) will enter.

    What makes one method better than the other? Is there experimental evidence or is this just a hypothesis ?

    • Pretty sure this is a myth. A fan facing outwards will draw air from the rest of your building (ie. warm air) to restore equal pressure, a fan facing inwards will draw air directly from outside.

        • As a much slower process, perhaps. It may draw from warmer pockets outside, or from upstairs. Point is it’s an unknown how long it would take to draw cool air from random sources inside the house, but it’s known how long it would take to bring cool air directly in the window from outside.

          You also have wind force, which is much more likely to push against your building than to pull air away from it, meaning a fan facing outwards is fighting the wind to move air, while a fan facing inwards is working together with the wind.

          When there are two ways of doing it, and one is slow and uncertain and the other is fast and sure, why use or recommend the former?

    • I can think of several conditions which would break the “fan blowing out = good” assertion.

      If you live in a block of units, a fan blowing out will replace air from the outside (via windows) but also from the internal ventilation of the apartment block, which will probably be warmer than the outside air. The result is that the average temperature of the replacement air will probably be a bit higher than the outside air temperature.

      If the fan is blowing in, all replacement air will be at outside temperature, which should result in a slightly cooler temperature.

      That said, it really needs some proper experiments to test, and given that the weather is different most nights, repeating experiments would be quite difficult. It’s very tempting to suggest this as a topic for Mythbusters…

      As I recall temperature tends to drop with lowered pressure, but I doubt that the change in pressure produced by a single fan would be noticeable.

    • Thermodynamics is why it works.
      Hot air travels to cooler areas basically.
      The fan facing out just provides circulation.

    • What i noticed is that when the fan faces out it creates quite a draft around its edges of air coming in most of which is blown out again. But when the fan blows in most of the air goes much further into the room and thus the cooling effect is not lost to recirculation. ie the leakage adjacent to the fan creats cooling loss when the fan faces outwards but dos not when facing inwards. Note that this is quite different from the pc situation where the fan is not relatively free standing.

  • I’ve often wondered about this. Wouldn’t you need a pretty big fan for it to work? I just imagine that if you have large windows wouldn’t there be more hot air coming in from around the fan than the fan would be forcing out? I feel like the fan would need to fit the window, or something. Also if this were true, would doing stuff like turning on the ventilation fan in the kitchen and bathroom help at all?

  • The hot inside air will naturally move outside to the cooler air (convection). Just make sure you have a few windows open around the house to allow for the flow of air. A stand up fan won’t have much impact on adding convection. You’re better off pointing the fan on yourself to aid your skin’s cooling via convection (sweat evaporation).

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