But your home has more that needs to be taken care of besides your homes air quality, but the HVAC itself. The HVAC (heating, ventilation, and air conditioning) system should be regularly cleaned and serviced to promote healthy air, but to also increase its longetivity. Over time dirt and other contaminants build up and cause the system to work much harder and in the longrun; shorten the life of the unit. Althought it's very good to replace the filter, the system gets dirty through everyday use. During winter you close all the windows and keep the heat in for the colder times, however this also trap in contaminants., so take that in addition to being quarantined; you might be in need of a duct cleaning.