# How does one create a draft in a room (with a single window)?

There is a room on the south side of the building, which doesn't have any ventilation vents, but does have a window.

Opening a window doesn't cause good air circulation (by which I mean that the air in the room is still hot, and the air on the street is still cold).

How does one create good air circulation in a room --with a single window- without using a fan or air conditioner?

• Apparently the question is about using the single window to create an air circulation inside the room. And I believe the question is asking for novel ideas and preferably "passive" systems that do not use electricity. is it? – Gürkan Çetin Jun 29 '15 at 16:42
• That's different then when I answered. If there was a breeze outside, there would be two options. First would be a vane - which, if the breeze was consistent enough, might be able to direct the cool air in. A second would be to employ a paddle wheel in the middle of the frame to allow the breeze to push new air in - not very passive. Finally, if you want non-electric but non-passive, a Stirling Heat Engine might be able to power a fan if the heat difference was enough. None of these are very "passive" in the sense of keeping your neighbors happy though. – Mark Jun 29 '15 at 17:18
• @ Gürkan Çetin, you're right! – PaulD Jun 29 '15 at 20:00

For simple ventilation, opening a single window may not mean a lot of circulation. Air has to come in and out of the same window, so it just leads to eddies and turbulence next to the window, with conduction doing most of the work.

Opening two windows allows a pathway for the air to flow in and out, and allows the air to mix in, which creates an open heat exchanger, fueled by the more effective convection.

• I'd say, if you open two windows (preferably on two different sides of a building) the flow is pressure driven. The pressure difference between the two sides of the building will cause the air to flow in at the high pressure side and exit on the low pressure side. – Knigge46 Jun 30 '15 at 12:44
• I wondered why this answer hadn't been down-voted for not answering the question, but I see that the "(with a single window)" was added to the Title shortly after this answer was submitted. – Ray Butterworth May 21 '19 at 12:39

The fundamental problem is that hot air must leave the room and cold air must enter it, both at the same time through the same single opening. The conflicting forces will mostly cancel each other out, resulting in very little actual exchange of air.

What you really need is old technology.

Double hung windows are what our ancestors used. The bottom sash lifts, just as in most windows, but the top sash, rather than being fixed, can be lowered to create an opening at the top.

With both a high and a low opening in the window, hot air tends to be forced out the top as cooler air enters at the bottom.

Raise the ceiling level in one side of the room, likely away from the window, this would allow a heat biasing movement vertically which would induce a very small air flow.