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

Fans like you’re talking about aren’t very good at pulling air in, they push the air from where they are (which in your case is inside). If you set it up “blowing in” it will be mostly blowing air that is already inside further inside. If you set it up “blowing out” it will be blowing air that’s inside mostly outside. Blowing out will be more effective, all things being equal. That said, it’s not always equal, if air is already being naturally sucked in with a window open, don’t fight it.