Usually, you will have someone that notices an odor inside the building that is noticeable when the HVAC system is on, or that some notice a difference in their breathing when they are inside the building versus outside the building. Whatever the reason is, if you have people inside the building noticing something off with the air quality, likely there is an issue with the indoor air quality and it is time to have some indoor air quality testing from Air Cleaning Technologies. They will test for mold, hazardous materials, lead, as well as other particulates that might be present in the air.