How many times a hour should you recirculate air in an hour?

Is it harmful to use bengay daily? What is 45 percent of 640? How many centimeters between brain and heart? How many 8ths in one quarter? Is it possible to have the value of relative permittivity less than 1? Do lakes and streams hold more than two thirds of earths freshwater? 10 plus 9 - 6 equals? How much is a trillion dollars times a trillion? A car traveling at 60 mph carries times the energy as the same car traveling 30 mph? How many degrees are there in a one-half turn? How do you Calculate the hardness of a water sample? How do you convert 0.74 ounces to a pound? When did Friedrich Gustav Carl Emil Erlenmeyer die? What is the formula for time? What book of the Bible has the word saint? How does Pi relate to the golden mean ratio? How do you write four thousand three hundred twenty one ten thousandths? What are the three type of fualt? What is 2.25 divided by 0.3? How do you solve -5n plus 9 equals -46?