Gas clothes dryer is venting into the crawl space
I don't like the "OMG" abbreviation and seldom  use it, but in this case OMG! It would have been bad enough to vent an electric dryer into a crawl (lint, moisture, fire danger), but to vent a gas dryer into a crawl is unconscionable. Gas dryers vent carbon monoxide. It interferes with your body's ability to transport oxygen.  If that seeps into the house it could create a myriad of problems, not the least of which is killing the occupants.   

Get that thing vented properly, regardless of the cost. Risking your lives on this failed setup isn't worth it. And clean out the lint, it's a fire hazard.