I like to think of it like emptying a bottle - if there's only a small hole it goes glug-glug, as occasionally air forces its way into the bottle. It's the sa

I like to think of it like emptying a bottle - if there's only a small hole it goes glug-glug, as occasionally air forces its way into the bottle. It's the same with air - there has to be a good way to get cold air in and hot air out with minimal turbulence from the two flows. I think you're better off blowing cold air in (there's no such thing really as 'sucking' in physics), as attempting to blow hot air out doesn't necessarily mean it's going to be replaced with cold air from the outside, rather than warmer air elsewhere in the building.