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I remember learning this in high school, but have forgotten it, and can't seem to find it anywhere online.

Air travels from areas of high pressure to low pressure...correct? So if I have a cold room in my house, does the air move from the warm rooms to the cold room or the other way around?

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up vote 11 down vote accepted

Air does indeed flow from high pressure to low pressure area (see the wind arrows on a weather chart), but in the case of two rooms the much more important effect is that of warm thinner air rising towards the ceiling when the air from the two rooms gets mixed.

Thus, cold air from the cold room will be leaving the room close to the floor (if the temperature difference is large enough you can actually feel it, otherwise you can use a candle to detect the direction of air movement). At the same time, warm air from the warm room will rise and move into the cold room close to the ceiling (again, sometimes you can feel this otherwise you can detect it with a candle). Similar air movements take place between your house and the outside when you open your house's door in winter or summer.

The tendency of warm air to rise towards the ceiling is actually exploited in floor heating. This was understood and taken advantage of already by the ancient Romans, see hypocaust.

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Actually, cold air just sinks while hot air rises (due to density of the collection of particles)... this "flowing" is just the wind pushing particles around, so you'll sense a change in temperature... if we want to talk about heat transfer (which I believe the question is really getting at), then "cold disappears" by "hot entering"... think about it, temperature in some sense is related to the speed of the collection of particles.

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Cold air flows downward according to hot air because it is more dense and sinks while hot air rises.

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In hot room the air will be much thinner thus reducing the pressure so the air flows from cold room to hot rooms.

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But isn't this forgetting the temperature dependence of the pressure? At constant pressure, hot air is thinner, but this assumes the pressure is equilibrated. – Ron Maimon Dec 30 '11 at 11:32

Cold air sucks out the energy of hot air! Moisture always is attracted to cold! The air in your room will move through the house as warm air leaves the room or house through cracks at ceiling height. Cold air will always come in through other cracks! Air goes out and new has to replace it! Seal the cracks around windowes doors light switch and plug plates and check the baseboards air can come in to the House through holes in the wall from attic or basements along the path of electric wires in the wall!

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protected by Qmechanic Dec 22 '13 at 16:38

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