Hello Stephen,
Our Jet Fan Attic Fan is only intended for ventilating attics.
The air you want to be its best is the room air…the air you have to breathe day and night. I would recommend that the attic air be sealed off from the house air and that the crawl air also be separate. You can ventilate the crawl space with a crawl-space-fan and the attic with the Jet Fan Attic Fan. Both spaces need to be dry, but you do not want that air running through your house. Keep in mind that vapor barriers have to be on the predominantly warm side of the insulation in wall and ceilings and floors and only one side. Does your HVAC do more heating or cooling? If the answer is cooling then the a single vapor barrier should go toward the outside of the insulation. And the opposite if heating is more common then it should go on the inside heated side of the insulation. One exception is the vapor-barrier you have on the ground in the crawl which you have done correctly to stop vapor before it gets into the space. Additionally, make sure there’s enough static venting in your attic, so when you Jet Fan comes on whether by heat or humidity (with optional humidistat) the “make-up” air will come from outside not from unknown places around the house. Same with any fan for your crawl…it must have “make-up” air from outside not from inside the house.Thank you for your interest in the Jet Fan Attic Fans,Jeff Tideman, “Jet Fan Man”