# Replace warm air with cold air

In summers i.e. now, my room has hot uncomfortable air in night, but outside air is cold 4-5 degrees Celsius colder than inside, my room has windows parallel to wind flow, so though wind flows in night it is parallel to my door. Keeping door open doesn't help either it does not replace warm air fast enough.

My assertion is that, if I keep a table fan near door will it help drive cold air inside? How feasible is this solution? Does fluid dynamics provide solution?

• if you put it on the doorstep it should, since it makes an underpressure behind the fan blades, Commented Mar 27, 2019 at 10:06
• Put a fan in the window and pull outside air directly into the room. Commented Apr 2, 2022 at 22:18

Depends on the wall material. For brick and concrete walls, the volume heat capacity of the walls is by powers of $$10$$ greater than that of air. To cool down the walls $$1 \, \textrm{K}$$ by air at $$-4 \, \textrm{K}$$ lower air from outside, you need a storm of $$50 \, \textrm{km}/ \textrm{h}$$ through the door for all of the night.
Fans cool the wet skin only. There is no effect of a stream of some $$\textrm{m}^{3}/ \textrm{h}$$ in a room of say, $$15 \textrm{m}^{2}$$ with $$30 \textrm{m}^{3}$$ air in it and some tons of hot walls around it.