As we have learned how to seal up our homes to keep out cold air in winter and hot air in summer, we have encountered the problem of getting fresh air into the home. When houses were drafty, had no insulated windows, were poorly insulated and weatherstripping was never used, fresh air was not a problem. Plenty was coming in the home. Trouble was, it was costing more to provide the heating or cooling. Tightening up the home reduced those costs but created bad inside air.