If your ducts or units are not cleaned often, so it is easy to accumulate dust in the ducts or unit, such as hair and dander, dust and dirt from the outside, fine hair falling off from clothes and carpet, insects such as spiders and beetles, construction and decoration garbage, and even the dead mice. These things can’t be cleaned out with the family vacuum simply, It can’t prevent dust and fine hair from circulating indoors.
If you have people with symptoms of asthma or allergies at home, this can exacerbate your condition if the indoor air is too dirty.