There is no recommended specific time schedule for duct cleaning. It depends on a number of factors such as the use of building/home, number of household inhabitants, pets, recent renovations, among others. Most people choose to clean their furnace and ducts as a personal decision and as part of their house cleaning schedule such as window washing, carpet cleaning, or other specialty cleanings services. There are some HVAC manufacturers that may recommend proper duct and furnace maintenance, which can include furnace and duct cleaning.  Sometimes Furnace and Duct cleaning can be a necessity such as when: Ducts are clogged with excessive amounts of dust and debris and/or particles are actually released into the home from your supply registers. Mold growth is suspected Dead insects or animals in the ductwork are suspected. Sometimes however the answer can be visible such as a dirty or clogged vent. [caption id="attachment_4110" align="alignnone" width="800"] A dirty and clogged air vent may prevent proper airflow[/caption] In addition to the above, there can be other signs that might indicate your ducts are dirty.