I assume you are looking at Scamp19 Deluxe, in which the bathroom separates the loft from the "living room". This separation keeps the fan noise away from the sleeping area. If you leave windows
closed, except those in the loft, the fan will pull or push plenty of outside air in both modes - in or out. The disadvantage is that you cannot reach up and change the speed or turn it off. Somebody has to climb down and flip that switch, although you can regulate the air flow by opening or closing the windows
, or the roof vent without getting up.
A related issue is this: The air exchange between the living room area and the loft is restricted by that bathroom, which makes the loft colder in the heating season. People have used small fans to move the air internally to alleviate this problem. I fixed it with a pair of 12Volt fans built in and wired so they turn on when the furnace