HOW RADON ENTERS
I heard someone say once...."My house sucks!" Coincidentally, this is actually quite true about most houses! Warm air rises! When the air in your home "escapes" up your chimney or through your attic, it must be constantly "replaced". This creates a vacuum in your home called the "stack effect". The "strength of vacuum" varies slightly from house to house. When air enters the return duct in your air handler it must be "drawn" from somewhere! When air is taken from one place (nature abhors a vacuum) and air rushes in to replace it! The air that replaces it must itself come from somewhere. That same "vacuum" pulls it inside the house. If there are cracks in the slab, wall cavities, openings around plumbing piping, cinder block walls or floor drains, air (and radon) can be drawn inside!
The air pressure within a house decreases with height, so the air pressure on the ground floor is higher than the air pressure on the top floor. Air always flows from areas of high pressure to areas of low pressure. During the winter, the difference in air pressure between the ground level and the top floor of a two story house will be a lot more severe outside than inside, where the air is warmer and less dense. Cracks and openings throughout the building shell allow the pressure difference between the indoor and outdoor spaces to drive air OUT of the top floor and to SUCK air in throught the first floor. The greater the difference between the indoor and outdoor temperatures, the more significant this airflow becomes.
Radon is pressure driven!....meaning that it has to be "drawn" inside your home! Typically, in a "negative pressure" in most houses caused by the HVAC system. When the air in your home is "sucked" into a "return vent" and eventually "conditioned" (heated or cooled) and put BACK into your home, that air has to come from somewhere. Each HVAC system has its own specific degree of "vacuum". It the vacuum generated by an air handler cannot suck enough air in the "room" to meet its "hunger" then air is pulled to it from other places. Most houses are NOT "air tight" so air will be drawn from "leaks" in your attic, your walls, around doors and windows and from your crawl space. This is how RADON enters your home. It is not PUSHING its way inside, it is being DRAWN in!
HOW RADON CAN ENTER YOUR HOUSE:
1. Cracks in concrete slabs
2. Spaces behind brick veneer walls that rest on uncapped hollow-brick foundation
3. Pores and cracks in concrete blocks
4. Floor-wall joints
5. From exposed soil, as in crawl space or sump pump
6.Weeping (drain) tile, if drained to open sump
7. Mortar joints
8. Loose fitting pipe penetrations
9. Open tops of block walls
10. Building materials such as some rocks
11. Water (this only happens in some cases with "well water")