With Bernoulli’s principle in mind (I think that’s the right one), is it more efficient to vent a room by putting a fan back from a window a bit, or right up next to it, and if so, is there a general sweet-spot as to how far back it should be?

Question

For context, this would be to vent a basement bathroom with a a window in an old house, and I can’t install a bathroom vent.

In: 857

Answer 1

Keep it back a bit. This is why:

In short:

Having the fan directly at the window expels the amount of air the fan moves, at the speed the fan moves it. This amount times this speed gives you x volume pr unit of time.

Having the fan back a bit, expels the air the fan moves PLUS a significant amount of air around it (since air is “sticky” – look up “laminar flow vs turbulent flow over aircraft wings” for instance). This reduces the speed of which the air os beeing ejected, but not by as large a factor as the volume being moved is increased. As such, this y volume pr unit time is significantly higher than in the first case, all other things being equal.