With the U.S. Environmental Protection Agency estimating that most people spend between 60 and 90 percent of their time indoors, the need for fresh, clean air is very clear. Understanding the need and meeting it, however, can be two very different things. Fortunately, there are many things people can do to enjoy fresher and healthier air inside their homes: from developing a good cleaning routine to using air purifiers, from ventilating a house to replacing vacuum filters. One very important task not to be overlooked is the air conditioning and heating system cleaning.