Moderator Post (s) for this thread: >ventationbyBillhart on 08/12/2007
How do you know that the air is "unsafe" now? What are the problems are symptoms?
What is the age of the house? The construction? What is the location?
One common solution is to use a the bathroom vent fan. Use a quiet one. And you can use a automatic timer, on the light switch, and or get a two speed fan. Slow for air exchanges. Hight to vent out the bathroom after using.
Then if the house is tight you need to install a connection for makeup air.