I have a wonderful little (16 x 14 x 8) test cabin at Bristol Community College in Fall River, MA. There are 3 'rooms', one of which stands in as the bathroom. It has a bath fan in the ceiling and a small, hopper window. When I depressurize the house to 50 Pascals, the pressure between the bathroom and the main body of the cabin is just 4.3 Pascals. When I stand in the bathroom with the door closed, air is pouring in through the bathroom fan, there is enough flow to make the fan rotate backwards! Doesn't that mean that the room is well connected to outside? Shouldn't the pressure in the room WRT the main body be closer to 50?