• Most crawl spaces have vents
  
  Model codes call for one square foot of opening per 150 square feet of surface area of crawl floor.
  Adding vents can have some beneficial effect provided they are not closed and do not cause frozen pipes.
  
  
• Blowing air into a crawl can cause freezing problems and still force some radon into home.

Crawl Space Depressurization

Useful for dealing with inaccessible crawls. Applicable in temperate climates, or buildings whose floors can be well sealed.

Copyright 2000, Great Lakes Center for Occupational & Environmental Safety & Health, School of Public Health, University of Illinois at Chicago