Which method is more effective (and why) for recirculating air into a room: a) using a fan to blow air out of a window, or b) using a fan to blow air in through the window?

Question

For context, I’ve got a basement room in an old house that isn’t tied in to central air conditioning, and sometimes the air gets a bit stale.

It has a basement window, so I’ll open that up and stick a fan in the window to blow air out, but someone told me that it’s better to have the fan outside and pulling fresh air in.

The room won’t be overpressured as it’s got a big gap under the door, and the fan doesn’t cover the whole window.

In: Physics

Answer 1

I’m assuming your goal is to cool the inside air down.

If the air outside is cooler than the air inside, it’s more efficient to open two windows on opposite sides, with the fan blowing outwards in one of them. This directly pushes the warm air out and indirectly sucks replacement air from outside.

If the air in the house above the basement is cooler than the basement or the outside air, then open one window with the fan blowing outward and open the basement door to allow cool air to flow in.

In general, it’s more efficient to orient fans to blow outward to cool homes down, but the difference is pretty miniscule.