 it can be contaminated. You can have radon, you can have dust, you can have mildew or mold spores in that air. So generally, we don't use the basement air as a source for air. Pretty much let the HVAC system do that. If the basement is finished, then you could have a return duct down there that pulls air from the basement into the HVAC system, but it wouldn't be a supplemental system by itself. Does that make sense?