There's lots of things to consider. The outside ambient air temp. The inside air temp. The room they are in. Is there A/C inside? how many S1s? etc
You can vent the heat out the window just fine, but you'll likely need an extra fan to push/pull the air out otherwise you just made a smaller room with even less airflow than you began with. The fans are big enough to pretty much only move air through the size of the Antminer S1 and maybe a foot or two more at best. Ideally, the outside air temp should less than the temperature of the enclosed room in which the S1s resides, if not you could end up raising the ambient temperature which will raise net temps.
You'll want to seal it up nicely so that if you do have A/C you're not trying to cool the outside as well as the room. Also, you'll want to PULL the air out of the room so that the AC leaves fresh cool air for the intake. A single fan at the window attached to the exhaust hose/vent would be plenty. You just want to ensure that the air is actually be exhausted out of the room and not being trapped in the room+hose. On a dryer vent this is fine because they don't run anywhere near 24/7 and builders don't care if you're temporarily creating a sauna in your dryer room or heating your crawlspace.
If you really want to get slightly more specific for the exhaust fan you'll need, (130CFM (stock fan) x # of Antminers)*10% for losses. Going bigger on the exhaust side isn't a problem, as it'll lower the pressure in the hose, letting the intake fans work easier for the same amount of air moved.