Poor polluted indoor air best can link to many fitness problems... Don't be surprise!! Tons of dirt mites, germs and bacteria's, rodents and insects are infested in your Air duct by myself with other contaminating airborne and widespread mildew inner the tough surface of your heating and cooling system, those aspects will spared in the complete dwelling region through the duct vents and causing many sickness and allergic reaction reaction particularly for little kids, pets and aged people.