What builds up in an Arizona air duct

A duct system has no way to clean itself. Air moves through it, and anything the air is carrying that is heavier than the airflow can hold eventually stops moving and stays. In a house in Scottsdale or anywhere else in the Phoenix area, four things make up almost all of it.

Fine dust gets into a house through doors, windows, attic hatches and every gap around them. Your return ducts pull house air back toward the air handler, so they see that dust before the supply side does.

This is the easiest thing to check yourself. Find a return grille, the big one, usually in a hallway or a ceiling. Look along the louvres in raking light. If there is a grey fur along the edges, that is what the return duct behind it has been drinking.

Drywall sanding produces a dust so fine it behaves like smoke, and sawdust is not far behind. If building work happened in the house with the system running, the return side pulled it in and distributed it.

In a newly built house it is usually worse, not better. The system often ran during the final weeks of construction with no filter or a builder-grade one, and the ducts collected the whole job.

Hair is light enough to travel and sticky enough to stay once it lands. It collects on the return side and at the bends of branch runs, where the airflow has to change direction and slows down.

This is the reason most people call after moving. Cooking residue, smoke, and years of somebody else’s dust are all still in the ductwork when the keys change hands, because nothing about a sale disturbs them.

Take one register off with a screwdriver and look at the inside lip and as far down the run as you can see. What is on that lip is a fair sample of the rest.

It will not tell you about the trunk line or the far end of a run, which is where a camera or a cleaning comes in. But it will tell you whether the question is worth asking, and that is usually all you wanted to know.