Tight closets, short runs and crowded attics
In compact houses the duct runs are often short, but they are packed into a small attic space with wiring, insulation and sometimes old equipment left behind. That makes access the main challenge. A closet air handler with only a hand's width of clearance takes patience and the right tools.
Return grilles are frequently in hallways, where they pull in whatever floats through the house. Filters that go unchanged for a season let dust pass through to the blower and coil. The fix may be as simple as cleaning the blower wheel and returns, and we say so when that is all that is needed.
